Module [mod_flexicontent] image Processing method: none

Thanks for the detailled tips. I do it exactly the same way only without the popup option and I respect the aspect ratio as well. Therefore Im sure it was the FC content module itself that screwed up the thumbs.
With the FIELD[image] within the FC content module its all good now.

ps: there is some lorem ipsum in this page:

True, its a dev installation and under construction.