Steps to reproduce:

1. Create new drawing and fill it with some contents that's easy to distinguish, for example text "DRAWING 1".
2. Save it as dr1.dxf
3. Close it
4. Open dr1.dxf
5. Edit it, for example change text from "DRAWING 1" to "DRAWING 2"
6. Save changed file as dr2.dxf
7. Close it
8. Open dr1.dxf (it should have content "DRAWING 1")
9. Open dr2.dxf (it should have content "DRAWING 2")
10. Close tab dr1.dxf
10.1 Qcad will ask you to save changes.
10.2 Press "Yes" --> nothing happens, dialog doesn't disappear.
10.3 Press "Discard" --> dialog disappears, tab gets closed
10.4 Tab that has content of file dr2.dxf ("DRAWING 2") remains open but gets title "dr1.dxf" (!)
11. Close tab
12. Press "Yes" in dialog that asks to save changes

Results:
1. Open dr1.dxf
2. Open dr2.dxf
As you can see, both files have equal contents ("DRAWING 2")

Expected results:

1. Files have their own contents.
2. Dialogs asking to save files disappear when checking "Yes", "Cancel" or "Discard"
3. Tabs don't change titles and associated file names when other tabs are closed.