(In reply to Matt Whitlock from comment #10)
> Whenever a context menu in Chromium fails to display correctly (shows as
> solid black instead), the following lines (or similar) are appended to the
> kernel message log:
> 
> nouveau E[chrome[5932]] multiple instances of buffer 249 on validation list
> nouveau E[chrome[5932]] validate_init
> nouveau E[chrome[5932]] validate: -22
> 
> Does not happen upon display of corrupted tooltips, only context menus.

I suspect you were using libdrm 2.4.60. Use either .59 or .61 and that
particular error will go away. That said, I also see the tooltip fail in chrome
on a GF108 (nvc0 driver) for a few versions of chrome now.