2.1.108 [CSS-Level2-2009] Section 17.5, Visual layout of table contents
The specification states:
Note. Positioning and floating of table cells can cause them not to be table cells anymore, according to the rules in section 9.7. When floating is used, the rules on anonymous table objects may cause an anonymous cell object to be created as well.
Quirks Mode and IE7 Mode (All Versions)
The floating cell is removed from the table, but is not replaced with an empty cell.