User Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/43.0.2357.52 Safari/537.36 Steps to reproduce: An flexbox item (see sample: 'main/left/main') can't shrink if the result would be an overflow (because of the child element 'block'). Even 'overflow: hidden;' is ignored. Actual results: The sample layout don't shrink to the window size, the height of 'main/left/main' is never smaller that the height of the 'block' element. Expected results: The sample layout should shrink to the window size. The 'main/left/main' div should shrink to height zero if the window is very small.

Note: The User Agent I've used to submit the bug (Chrome) is not the User Agent I've used to reproduce the bug (Firefox 37)

Setting min-height:0 on the <div id="main"> makes it able to shrink down below its intrinsic height, as expected (the default value of min-height is "auto", not 0). As far as I can tell, that's per current spec. Sounds like Chrome's changes to update to the spec here are not complete yet.

Yeah, the min-content height of the outer "main" element is nonzero, so it needs "min-height:0" to override its default "min-height:auto", or else it'll be as tall as its contents' min-content size. Chrome (dev edition, w/ min-height:auto support) indeed doesn't seem to be following the spec here; I'll file a Blink bug.

Filed https://code.google.com/p/chromium/issues/detail?id=487302 on Chrome's rendering here.