I had the same problem with the latest version on Chrome 27.0.1453.94 m. Works fine in the previous version. The following workaround may help:
Click drop-down menu on top-right corner –> click “Settings” –> click “Show advanced settings…” on the bottom –> scroll to the bottom, and uncheck “Use hardware acceleration when available”. And restart the browser..
Are there any advantages/disadvantages to using hideMode:'display'? I too found that doing that solved the black square problem, and I'm considering just overriding Ext.menu.Menu to make it a default for all my menus. I don't want to run into any other problems though because of it.
Not really. The only difference between display:none and visibility:hidden is that visibility:hidden items still appear in the layout, but that doesn't apply to absolutely positioned things. Display:none would be a better default AFAICS