+1 i don't think the slider fix is the issue. i agree that it sounds like a kernel issue. you may want to try a different kernel (the same kernel will work differently on individual droids). as chewy said, you may want to ramp up your min settings in sleep mode. also, you may want to try messing with the sampling rate and up threshold in the advanced settings of cpu - i think that might play a part, too. check out the thread "overclocking 101" - VERY detailed (largely over my head), but if memory serves it has some discussion in there about settings for this type of issue.
i dont think its the slider fix thats the problem. the slider fix is just the stock Phone.apk and should work fine with all themes...
is your phone coming out of sleep mode when you answer the phone when this happens? if you have setcpu, try setting the min to 500 mhz for your sleep profile.
Today I started having problems answering my phone. phone rings, slider pops up, go to slide to answer and nothing. slide after slide and nothing. have to turn screen off then back on and then slide to answer works. flashing back to lithium stock and without slider fix to see if that solves it. have been having problems since installing slider fix. Has anyone else had this problem?