Debugger: Issues when adding / removing breakpoints while debugging especially while mixed debugging

Steps to reproduce:

• setting breakpoints while not debugging seems to be fine as it was before 4.8
• but when debugging it seems there are some issues
  • adding a breakpoint inside QML before the QML part gets executed does not always show the breakpoints on the line number (editor) - sometimes it works
  • the breakpoints seem to get added to the qml debugger, but may end up with wrong information (I had several times added qml break points at locations that should be able to get triggered - but the break points itself where located at property assignments of object creations and similar
  • removing break points seem to not remove them completely - I hit them still although they had been removed
  • removing break points might make the debugging session completely useless (had a breakpoint on app.exec(); of the cpp part and another bp on the if condition before, when the latter one got hit, removed the one on app.exec() and hit continue - but never came to a state where inferior could be interacted with - had to stop this by Stop on the Application Output pane