The left Windows key on the keyboard is no longer usable as a keybind and will instead perform the default action (opening the start menu).
Trying the same action on the latest version of Arma2: OA has the expected result and earlier versions of Arma 3 did so as well.
Some research on reddit shows this bug was introduced about 4 months ago [ https://www.reddit.com/r/arma/comments/3ngyn3/arma_3_broken_windows_key_bind/ ] and as far as I know has not been officially reported here.