Okay, I've tracked down the bug in your .cap. It's the CyclopodDroneDamaged object that's causing it. Or, more specifically, it's the Rotate behavior that's on the object. If you remove the behavior, the game runs fine.
Don't know why that bug is there, but if it's possible to recreate it in a smaller .cap then that would be the way to go. My advice is to remove the rotate behavior and spin your sprite manually with events.
[quote:2x69ovmy]This seems to instantly set the Sampling to point for everything (if the underlaying layer has Effects on it) resulting in crazy jaggies:
Try checking "Force own texture" on your layers. Another option would be to set the ship in the same layer as everything else and make an "Always -> Send to front" event.
[quote:2x69ovmy]Also - evilly exploiting your helpful nature - I'd like to have the ship mouse controlled, but with a 8-way like behavior = limited speed, slight acceleration and deceleration. Wonder if there's any way to do this without too many extra events
Here's an example that uses Custom Movement:
http://dl.dropbox.com/u/529356/mousecontrol.cap
v0.99.82
Hope that's the sort of thing you were looking for.