Why the confusing messages?

Write chat. I have a ready control to display messages. He works steadily when lying on the form, but when I try to put it in the TabControl begins to blunt. Messages from different tabs confused, error any climb periodically, the tabs are not visible, the messages... please Tell me what is the problem?

Code here is not got by the number of characters, so here it is: the control, ViewModel, and, markings.
July 9th 19 at 12:50

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