I too have been doing a lot of research on water chemistry lately and my understanding is you need a minimum of 50 ppm calcium for a proper mash. In addition calcium helps yeast to floculate after fermentation.
To my mind that is a very large temperature swing for the yeast to undergo in a few hours. They got the signal to go dormant. I've heard you can lower the temp a degree F an hour or so.
Sent from my Galaxy Nexus using Home Brew mobile app
A tenth of an ounce isn't going to do much for aroma. You need at minimum a full ounce, or more, to get anything noticeable. Then good news is you can still dry hop. Use 2 ounces at least.
Probably this, unless it goes on for an extended period of time, in which case it wasn't done fermenting and when you agitated the beer it restarted fermentation.