Draw handler sometimes not removed upon saving

[Nathan Craddock]

When saving a projectile .blend file with Draw Trajectories disabled, it appears that the handler is not actually removed. When the file is reloaded the trajectories are still drawn, and the checkbox has no effect.

Not sure if this is an issue with Blender itself or the addon. Other addons handle the draw handler similar to Projectile, so it isn't clear what exactly is happening.