Fermcap failure!

I used Fermcap for the first time for a Two-Hearted Ale clone I brewed on Father's Day. I made a 2L starter and used Fermcap during the boil, and it worked like a dream. I used it again on brew day for the boil, and again, it worked great, allowing me to boil 7.5 gal in my 8-gal kettle with no boilover. However, I used it a third time in the fermenter (6.5-gal glass carboy) just after pitching yeast and aerating with oxygen. I did not connect a blowoff hose because by then, I had faith in the stuff. Needless to say, I woke up the next morning to a huge mess after my airlock blew off and the carboy erupted foam like a volcano. I used the recommended 2 drops per gallon and then even a little extra, so I am wondering what the heck happened. Anyone else have a similar experience using Fermcap during fermentation?

Doesn't seem to work in my fermenter either (carboy). Works great in the boil kettle though.

I think the issue is that Fermcap doesn't stay in suspension. It only works if the liquid is in motion, keeping the fermcap in suspension. You don't want to add it when you pitch the yeast, you want to add it when fermentation starts taking off. In the boil there's tons of motion, and during fermentation there's plenty of churning motion. If the liquid is still, it sinks and doesn't do its job.

That makes a lot of sense. My next batch I'll experiment with that by waiting to add fermcap until things start rolling - but I will definitely still set up a blowoff hose...