Clarification: in an earlier iteration of the iRule I logged a specific message to the log file. I have since changed this, but it looks like the old logging directive persists. Curiously, the other parts of the iRule are not persisting (which is good!).
But I and others have seen some odd behavior when updating iRules on actively used virtual servers as described in the post. If you're able to reproduce the issue, you could open a case with F5 Support and ask them to help you investigate the issue.