I use eTrade but don't profess to know everything about it!
My understanding is that if you put your stop loss trigger at 19, but say "sell at market" it will put it through at the best price it can get. You can set a limit that you don't want to sell for less than as well ie if price drops to 10 and you wouldn't want to sell for that then you could set it at 15.
I also thought that with eTrade that their standard default stop loss was to put the sell order in "3 ticks below" the trigger price. In this case that would be 17.5. The reason for this is to ensure you don't miss getting sold for exactly the reason you mentioned, so it sounds like something went wrong.
Either A) you put the order in differently to the default, or incorrectly or B) eTrade has far bigger issues than just being slow this week and the stop losses aren't working properly which is entirely possible but a very scary thought.
