Good question, I have a similar problem. I usually copy all my new pics from the day to my PC when I get home at night. Lets say I have 20 pics on the phone, and I delete numbers 13 and 14. The next picture I take with the phone is 13, not 21 like it should be. It kind of fills in the gaps if there are any. So after a few days I have new pictures mixed in with my old ones.
My real camera just continues the numbers no matter what, even if I take the batteries out. I really wish the evo would do this.