SDL Events and Threads issue

I’ve been having a problem with my SDL app losing
focus and not getting it back, and finally narrowed it
down to something to do with threads:

If I only have a single thread running, everything
works fine.

If I have more than one thread running when my SDL
window loses focus, when focus is regained SDL doesn’t
seem to be getting events (mouse/keyboard).

Any thoughts what might be causing this? (Linux
with KDE).