I have a mag that will sometimes allow two rounds to be stripped off such that they jam together horribly and sometimes the bolt will just fly right over the top round leaving an empty chamber for the next trigger pull. I don't see anything wrong with the lips - although I know that does not mean much. Is it possibly a worn out spring? Bad follower (it is an anti-tilt)?

Any suggestions?

OK. Lets see. Does this happen with other mags?
If not, then its in the mag. Are the feed lips spread open more on one or the other? Is the mag bulged open near the feedlips?

just this mag. I can't really see anything wrong with the lips, but I'll check again.

Could be the spring.  If the spring is weak, the recoil can cause the top round to pop out of the mag because there's not enough force holding it in.  Then, when the bolt comes forward, it strips a second round off the top, and you end up with two floating around in there.  I was having this problem with some mags, replaced the springs, and solved it.  

Ok - double checked the feed lips and they appear to be fine. I am planning on buying a new spring and follower and seeing if that works.

If anyone has any other suggestions, please let me know!

Also - what is the best way to clean the inside of the mag while I have it apart?

I had the same thing happen with two mags I picked up from Brownells.  Based on the MagFAQ,I figured I would give them a try to see.  Everytime, the last two rounds would try to double feed and the bolt would skip right over them.  Also, if I tried to load 1 round, the round would stay for a second, but would then get pushed right out of the mag.  Wanted to check the feed lips, but can't find any dimensions for them.  

I was also wondering if perhaps the mag catch slot was cut too high on the magazine.  Haven't measured them yet, but when I compare to a USGI mag, the slot seems higher.  

Old toothbrush.