Seems the new 0.8.2 terminal is capturing the F10 key presses to show the (hidden) menubar. I have terminal (with multiple tabs), hidden menubar and Midnight Commander running. When F10 key is pressed in tab with MC the menubar and not the MC's "Exit" dialog appears.
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Go to preferences -> advanced and check the 'disable menu shortcut key (F10 by default)' and see if that fixes it?
Yes, it's that, thanks. Fortunately XFCE still keeps stuff configurable :-)