the editbox seems to allways attache to the default chatframe now, but i will monitor this for a few days since the problem occured very rarely - but now i got another problem:
on the second chatframe, the frame where the editbox would be is completely gone. in theory this is what i would like to achieve, but it leaves a empty space between the chatframe and the tab selector box (see screenshot)
the other 2 problems i had with chatframes work perfectly now