I'm not sure if this is one macro or two macros or three macros or what. If it is just one I could see mixing /follow with /startattack causing problems.
Other than that, I'd just say maybe they are taking the unintentional (and hazardous and annoying) "break" because they didn't have time to see who the focustarget was before you told them to assist. You may have noticed problems even before they were feral; sometimes it takes as long as .5 seconds for the focustarget to register on your alts because of slow network latency.
Just as a test I'd turn on "see target's target" on all of the alt windows and watch to see if the problem persists when you actually wait for the focustarget to register on all windows.