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Shadowcat: I just installed version 1.3.8 for Linux, and everything was running very smoothly up until the point where I had started the first level and scrolled the screen to the side.

A small amount of movement to either side causes the frame-rate to plummet to probably 4 or 5 FPS. If I manage to make it scroll back to the approximate starting position (it needn't be exact), the frame rate becomes completely smooth again. I can continue to alternate back and forth between good and awful frame rates by scrolling to or away from the original position.

For reference, the smooth range is approximately the positions in which the moon is not obscured by the movie theatre (ignoring the crane and the bits of building which do not overlap the moon). The moon can be *slightly* obscured by the building on each side, but definitely by the time half the width of the moon is obscured, the frame rate is definitely bad.

The game is consistently smooth within that range.

By contrast, the second level has a really terrible frame-rate from the outset!
Are you still getting this issue with version 1.3.9?