This goes away when selecting a table row. Probably bad CSS?
Created attachment 323024 [details] [SCREENSHOT] unexpanded table
Created attachment 323025 [details] [SCREENSHOT] selected a row
This happens for me on my iMac 5K retina screen.
On non-retina this only happens at super small widths (where the min-size of a column is not taken into account for columnWidths). Here it appears to happen at a wide width, so I suspect this because Retina has half pixel borders and the total width is calculated incorrectly. I'll look into this soon.
<rdar://problem/34858720>
Created attachment 323144 [details] [PATCH] Proposed Fix This fixes the issue for me on non-Retina. I'll have to test this on Retina before landing though to make sure I addressed the actual original issue.
Comment on attachment 323144 [details] [PATCH] Proposed Fix Looks good on Retina.
Comment on attachment 323144 [details] [PATCH] Proposed Fix r=me, verified on retina machine.
<https://trac.webkit.org/r223059>