Created attachment 62767 [details] Reduced test case This is a little hard to describe, so please see the test case attachment. When: 1) one row of the table contains a colspan, and 2) another row has one or more cells with 'display:none', and 3) an item in one of the visibly displayed cells has a :hover style that changes its geometry (by changing padding, width, etc.), then: The non-hidden cell in the row that contains the hovered element will suddenly jump to a much smaller width if the table is 100% width. If the table is auto width, the colspan row jumps to be about twice the size of the other row. It then never goes back to its original width. This test case was painstakingly reduced from a set of complex pages that exist in a production online banking Website at a credit union (a banking account is required in order to sign on to see it though). It only occurs in somewhat recent nightly builds, probably within the last week. It does not yet show up in the shipping version of Safari. It does pretty much ruin the layout of that site though, so I'd classify it as pretty severe.
It looks like this got fixed.