Moom user Craig Grannell mentions an odd bug he discovered that affects Moom and other window management apps:

I also recently discovered an issue with window manager Moom, where windows wouldn’t snap, but would instead skid around the display, triggering motion sickness. It turns out other window managers are affected, and the trigger is activating text-to-speech.

Basically, if you use text-to-speech and then use Moom within the same app, you’ll find that Moom behaves in strange and ugly ways: windows slowly wander to their new positions, and you can’t resize and move (i.e. use the grid), as only one of the two operations will complete.

The issue, unfortunately, lies in OS X not Moom, so it’s not something we can fix. However, there are two workarounds detailed in this blog post.