Subclasing QAbstractItemModel Issue

[wolfi3b]

Hi,
im working on one application and I need to subclass QAbstractItemModel. I googled which methods I need to reimplement to make it work. Basic Idea is I need to reimplement mainly data methode (the others just to do the same as usualy), to choose what is returned. Problem is, if I return anything else than simple QVariant(), for example if I return 1 (I also tryed conversion of everything I tryed straight to QVariant befor returning) result looks like this:

Im not able to figure out from where these checkboxes appeared there. I can return anything, and still, here they are. Its different when I return like 0 or 1. On 0 its unchecked on 1 its checked. But still, I cant figure it out.

I know maybe I just forgot something basic, or Im just blind to see the problem and it can be something realy simple, but I tryed for some time and Im out of ideas.
Can please anybody help me with this? I would realy appreciate any help.

PS: I put this class in simple project, sou if needed, you can try to run it and see what it is doing.