"hamburger" second-level popups make the cursor vanish?

[hobbitalastair]

When hovering over, say, "hamburger"->bookmarks, the bookmarks submenu appears, but then the cursor vanishes, and doesn't reappear.
It doesn't seem to be moveable either, since I can't make anything else highlight. Swapping to a VT and back makes the cursor reappear and work again, but then the submenu options don't appear to be selectable...
The typing cursor in the URL bar (on the "new tab" window) still blinks however, so it doesn't appear to be a freeze.

[hobbitalastair]

Still the same as of SouthSister.