In Webkit, if a table contains a cell with "colspan" attribute, automatic table layout algorithm needs to transfer its minimal width constraint to all the columns it spans. The algorithm contains a step to distribute the minimal width constraint to columns in proportion to their maximum width effMaxWidth (in AutoTableLayout.cpp: AutoTableLayout::calcEffectiveWidth()). For those columns that have a pecentage width, this width doesn't affect the effMaxWidth and isn't considered in this minimal width distribution process. This may affect the final table layout.
IE and Firefox both work fine in this scenario. Please refer to the attachment for an illustration.
However, since "UAs are not required to implement this algorithm to determine the table layout in the case that ¡¯table-layout¡¯ is ¡¯auto¡¯; they can use any other algorithm even if it results in different behavior."(CSS2 220.127.116.11). I am not sure whether we should modify the algorithm.
Created attachment 18340 [details]
An example for the problem.
The test case is pretty clear if you open it up in Firefox as well.
Given that we differ from IE and FF in this test, I would suggest we change our behavior. Especially if this can actually be found on live sites.