Vissa, I'm back.
It's been a busy winter holiday season for me.
I just poked around your English category and something caught my eye... "Category is Open for Images" was turned off. I then poked around the source code and, sure enough, if that option is turned off then it is suppressed from the list of valid categories.
What exactly was occuring when you had "Act as category" turned off and "Category is open for images" turned on? Was it a style issue or something else?