Many thanks to Molloy first, so obviously it looked like, I probably would not have seen it this way. But FXCM told me (on the phone) that they simply had an error in their system and that they will pay for the property damage. I'm just looking forward to this.
So, if there are any other FXCM users with EUR/CHF long trades being stopped on prices lower than 1,20 on 17/12/2014 now it is the right moment to get some money back.
@jcl: maybe this info is worth for a 'newsletter' at the Zorro users?