Persistence should just work in conjunction with CMP. There is no command to alter this behavior.
Two things jump out at me here. First, you said that you disabled CMP on this virtual but still saw log entries from both tmms. That says to me that that virtual was still running in CMP mode. You might want to try re-enabling CMP globally and re-disabling it on that virtual, and then run "bigstart restart" or perform a reboot and see if the problem recurs. Second, if all you're looking for is vanilla source IP persistence, then I'm not sure why you're using an iRule at all. It might work better if you just configure a persistence profile.
All that said, if you're still having a problem with persistence, and disabling CMP fixes the problem, then I would definitely open a case with F5 support.