Qt Quick Designer freezes when changing document, while qmlscene is running (qmlproject) on Windows

When I have a qmlproject open, launch the application via "Play" in qmlscene, and start editong in Qt Quick Designer, the tool sometimes freezes for several seconds. This mostly happens when going into or out of components, sometimes with simple document changes.
It does NOT happen while dbgview runs, or Qt Creator is being run in the debugger, or when launched from an IDE.
There seem to be several szenarios where the freeze can occur. Here a very easy-to-reproduce one:

1. Enable the debug view in the Qt Quick options
2. Open a qmlproject with several qml.ui files
3. launch qmlscene (press play)
4. change the current document
5. -> Freeze

There are 5 processes involved:

• Qt Creator (or Design Studio)
• 3x qmlpuppet
• qmlscene
  My assumption is that some "pipe" is filled with data which somehow blocks the other processes. Here is the output in dbgview

  [3168] End Process:  3168
  [11744] End Process:  11744
  [6716] "Debug view is enabled"
  [9376] Loaded default dummy context object.
  [8104] Loaded default dummy context object.
  [11844] Loaded default dummy context object.
  [8104] QWindowsWindow::setGeometry: Unable to set geometry 0x0+1120+520 on QQuickView/''. Resulting geometry:  232x0+1120+520 (frame: 13, 58, 13, 13, custom margin: 0, 0, 0, 0, minimum size: 0x0, maximum size: 16777215x16777215).
  [8104] QWindowsWindow::setGeometry: Unable to set geometry 0x0+1120+520 on QQuickView/''. Resulting geometry:  232x0+1120+520 (frame: 13, 58, 13, 13, custom margin: 0, 0, 0, 0, minimum size: 0x0, maximum size: 16777215x16777215).
  [11844] QWindowsWindow::setGeometry: Unable to set geometry 0x0+1120+520 on QQuickView/''. Resulting geometry:  232x0+1120+520 (frame: 13, 58, 13, 13, custom margin: 0, 0, 0, 0, minimum size: 0x0, maximum size: 16777215x16777215).
  [11844] QWindowsWindow::setGeometry: Unable to set geometry 0x0+1120+520 on QQuickView/''. Resulting geometry:  232x0+1120+520 (frame: 13, 58, 13, 13, custom margin: 0, 0, 0, 0, minimum size: 0x0, maximum size: 16777215x16777215).
  [9376] QWindowsWindow::setGeometry: Unable to set geometry 0x0+1120+520 on QQuickView/''. Resulting geometry:  232x0+1120+520 (frame: 13, 58, 13, 13, custom margin: 0, 0, 0, 0, minimum size: 0x0, maximum size: 16777215x16777215).
  [9376] QWindowsWindow::setGeometry: Unable to set geometry 0x0+1120+520 on QQuickView/''. Resulting geometry:  232x0+1120+520 (frame: 13, 58, 13, 13, custom margin: 0, 0, 0, 0, minimum size: 0x0, maximum size: 16777215x16777215).
  

  Note the "Debug view is enabled" which comes from Qt Creator. When removing that, the freeze seems to be gone! See change on codereview.