Have you looked at variability of price movements (including...

Have you looked at variability of price movements (including intraday movements) of the stock in question to make sure 12% isn't in the bounds of normal volatility?

Presumably you would be aware that there are people out there who delibereately drive prices down in expectation of triggering stop losses so that they can pick up more.

Also, I don't know if it happens with Etrade but with Commsec I have had a trigger (although it wasn't a stop loss) get fired when the stock was nowhere near the trigger point.