Just a few questions to see if you have the exact same symptoms I have:

1. If you set fps_max to 60, what is your frame rate? I get 32.
2. If you set fps_max to 200, what is your frame rate? I get 63.
3. If you set fps_max to 360, what is your frame rate? I get 270.
4. Finally, in a level containing a small block and a single entity, is your frame rate static or does it fluctuate wildly? Also, is the motion very jerky? In my case, it fluctuates wildly and all motion is very jerky.

If all of these are true for you, then you're experiencing the exact same symptoms I am. When I freshly installed Windows XP, I never had this. Until I double-clicked an AVI, which opened up Windows Media Player (of which I wasn't expecting), the frame rate was behaving normally. Upon doing so, it always has done this and no matter what I do, I cannot prevent it. It makes running experiments much less reliable.

"You level up the fastest and easiest if you do things at your own level and no higher or lower" - useful tip My 2D game - release on Jun 13th; My tutorials