I have noticed that Reaper on OS X steals spacebar keystrokes when typing into a TextEditor component in my plugin. Pressing spacebar will toggle audio playback in Reaper, even when the TextEditor has focus.
I have observed the same behaviour in a couple of commercial Juce plugins, so I assume that the problem is not unique to me.
I also found a thread in the Reaper forum where someone describes the same problem: https://forum.cockos.com/showthread.php?t=205497
That thread includes a Reaper-specific solution, but it would be great if it was possible to type spaces into a TextEditor without workarounds.
I haven’t noticed the same behaviour in non-Juce plugins (e.g. u-he’s plugins).