UploadItems EWS operation does not work properly for public folders.

Question

Perform the following on an Exchange Online deployment -

1. Create a Primary and Secondary public folder mailbox, with a folder on each of the mailbox. Powershell will have to be used to create such a folder.
2. Using impersonated access, download items using ExportItems EWS operation. Make sure to use a user which has its PublicFolderInformation property (from GetUserSettings operation) configured to secondary public folder mailbox.
3. Use a post from the folder on the primary mailbox to call the UploadItems EWS operation with the UpdateOrCreate operation.

It has been noticed that a duplicate post is created for such an item, even if a post with the same id is present in that folder. Calling with "Update" instead of "UpdateOrCreate" fails with "item not found" error.
Making a GetItem EWS call with same id returns that item.

Server Version Info returned
MajorVersion="15"
MinorVersion="20"
MajorBuildNumber="3868"
MinorBuildNumber="33"
Version="V2018_01_08"

Can someone let me know, what could be wrong?