Hi Al
Yes I know, and this is why I am asking people to experiment with flexbox.
The fix for IE10 is to give the right hand sidebar, (or the content) a larger flex-grow property, the bug is caused by the flex shorthand property not recognizing % values, and using the flex-basis as a set width instead of a preferred size.
I have logged the bug, (and many others) with the various browser bug bases.
This and other bugs, do have 'fixes', so I hope users will experiment with flexbox and provide feedback.
Flexbox is no different than any other css feature, "we can only find the problems in actual use".
Strangely enough, I have found the most consistent to use is the old 2009 implementation on mobile devices, (no doubt iOS7 will change all that ).
PZ