When the project window isn’t active (the mixer is for example), the start/stop with the spacebar doesn’t function anymore, also the 1 of the numpad which sets the cursor to the first locator (begin of the song) doesn’t work anymore. They only work when activateing the project window.
Bad for the workflow this …
Working fine here.
Will try a different keyboard, not a logical desicion as it works when the project window is activated, but it works for you when the project window isn’t activated, so the problem lies probably in my setup how weird this may sound to my own ears 
Its works fine here in the mixer, in audio editor, key editor, drum editor, so yes it seems to a problem with your setup.
Maybe try to trash preferences.
Check your Key Commands to verify the spacebar didn’t accidentally get reassigned. Probably not, but worth double checking.
Thanks, the trash prefs did the trick (obviously also deletes all custom keys defs).
Happy now because I was using a EditorsKeys board which I do not want to replace.