Debug mode does not respond to key F10

Launch and compile any simple C++ program.
Keys F5, F7, F9 and F11 all work as advertised.
Key F10 does nothing – it should single step through a function.

I discovered that alt-D, then F10 does work, but only when the Debug menu pulled down by this is active. When the debug menu is inactive, F10 no longer works. The Debug menu also works through a mouse click.

I suspect that F10 has been redirected somehow, but cannot find a dynamic map of keys to their operations.
This is with fakeVIM disabled, though this also happens with fakeVIM enabled.

Not a fatal problem, but a real nuisance, since stepping through a section of code in trouble now requires a lot of mouse operations or extra key strokes.