Runtime Changes for Migration from .NET Framework 4.5.1 to 4.5.2

If you are migrating from the .NET Framework 4.5.1 to 4.5.2, review the following topics for application compatibility issues that may affect your app:

ASP.NET

ASP.NET MVC now escapes spaces in strings passed in via route parameters

Details In order to conform to RFC 2396, spaces in route paths are now escaped when populating action parameters from a route. So, whereas /controller/action/some data would previously match the route /controller/action/{data} and provide some data as the data parameter, it will now provide some%20data instead.
Suggestion Code should be updated to unescape string parameters from a route. If the original URI is needed, it can be accessed with the RequestUri.OriginalString API.
Scope Minor
Version 4.5.2
Type Runtime
Affected APIs

No longer able to set EnableViewStateMac to false

Details ASP.NET no longer allows developers to specify <pages enableViewStateMac="false"/> or <@Page EnableViewStateMac="false" %>. The view state message authentication code (MAC) is now enforced for all requests with embedded view state. Only apps that explicitly set the EnableViewStateMac property to false are affected.
Suggestion EnableViewStateMac must be assumed to be true, and any resulting MAC errors must be resolved (as explained in this guidance, which contains multiple resolutions depending on the specifics of what is causing MAC errors).
Scope Major
Version 4.5.2
Type Runtime

Profiling ASP.Net MVC4 apps can lead to Fatal Execution Engine Error

Details Profilers using NGEN /Profile assemblies may crash profiled ASP.NET MVC4 applications on startup with a 'Fatal Execution Engine Exception'
Suggestion This issue is fixed in the .NET Framework 4.5.2. Alternatively, the profiler may avoid this issue by specifying COR_PRF_DISABLE_ALL_NGEN_IMAGES in its event mask.
Scope Edge
Version 4.5
Type Runtime

Data

SqlConnection.Open fails on Windows 7 with non-IFS Winsock BSP or LSP present

Details Open() and OpenAsync(CancellationToken) fail in the .NET Framework 4.5 if running on a Windows 7 machine with a non-IFS Winsock BSP or LSP are present on the computer.To determine whether a non-IFS BSP or LSP is installed, use the netsh WinSock Show Catalog command, and examine every Winsock Catalog Provider Entry item that is returned. If the Service Flags value has the 0x20000 bit set, the provider uses IFS handles and will work correctly. If the 0x20000 bit is clear (not set), it is a non-IFS BSP or LSP.
Suggestion This bug has been fixed in the .NET Framework 4.5.2, so it can be avoided by upgrading the .NET Framework. Alternatively, it can be avoided by removing any installed non-IFS Winsock LSPs.
Scope Minor
Version 4.5
Type Runtime
Affected APIs

Entity Framework

EF no longer throws for QueryViews with specific characteristics

Details Entity Framework no longer throws a StackOverflowException exception when an app executes a query that involves a QueryView with a 0..1 navigation property that attempts to include the related entities as part of the query. For example, by calling .Include(e => e.RelatedNavProp).
Suggestion This change only affects code that uses QueryViews with 1-0..1 relationships when running queries that call .Include. It improves reliability and should be transparent to almost all apps. However, if it causes unexpected behavior, you can disable it by adding the following entry to the <appSettings> section of the app's configuration file:
<add key="EntityFramework_SimplifyUserSpecifiedViews" value="false" />
Scope Edge
Version 4.5.2
Type Runtime

Opt-in break to revert from different 4.5 SQL generation to simpler 4.0 SQL generation

Details Queries that produce JOIN statements and contain a call to a limiting operation without first using OrderBy now produce simpler SQL. After upgrading to .NET Framework 4.5, these queries produced more complicated SQL than previous versions.
Suggestion This feature is disabled by default. If Entity Framework generates extra JOIN statements that cause performance degradation, you can enable this feature by adding the following entry to the <appSettings> section of the application configuration (app.config) file:
<add key="EntityFramework_SimplifyLimitOperations" value="true" />
Scope Transparent
Version 4.5.2
Type Runtime

Windows Presentation Foundation (WPF)

Calling DataGrid.CommitEdit from a CellEditEnding handler drops focus

Details Calling CommitEdit() from one of the DataGrid's CellEditEnding event handlers causes the DataGrid to lose focus.
Suggestion This bug has been fixed in the .NET Framework 4.5.2, so it can be avoided by upgrading the .NET Framework. Alternatively, it can be avoided by explicitly re-selecting the DataGrid after calling CommitEdit().
Scope Edge
Version 4.5
Type Runtime
Affected APIs

Intermittently unable to scroll to bottom item in ItemsControls (like ListBox and DataGrid) when using custom DataTemplates

Details In some instances, a bug in the .NET Framework 4.5 is causing ItemsControls (like ListBox, ComboBox, DataGrid, etc.) to not scroll to their bottom item when using custom DataTemplates. If the scrolling is attempted a second time (after scrolling back up), it will work then.
Suggestion This issue has been fixed in the .NET Framework 4.5.2 and may be addressed by upgrading to that version (or a later version) of the .NET Framework. Alternatively, users can still drag scroll bars to the final items in these collections, but may need to try twice to do so successfully.
Scope Minor
Version 4.5
Type Runtime

WPF spawns a wisptis.exe process which can freeze the mouse

Details An issue was introduced in 4.5.2 that causes wisptis.exe to be spawned that can freeze mouse input.
Suggestion A fix for this issue is available in a servicing release of the .NET Framework 4.5.2 (hotfix rollup 3026376), or by upgrading to the .NET Framework 4.6
Scope Major
Version 4.5.2
Type Runtime