In the PlayerMoveEvent, if I call event.setTo(), it sets the "to" Location in the PlayerMoveEvent, but does not actually change the location. I've disabled all plugins except for the plugin that sets the to, and PlugMan. I've tried this on both Spigot and Bukkit.

E.g.
Location to = event.getTo();
to.setPitch(0F);
event.setTo(to);

That wouldn't work. I've tried with multiple different event priorities. I'm sure the event listener is registered (tested).