Answer by Jimmy F for Visual Studio 2010 annoyingly opens documents in wrong MDI pane

I had the same problem with Visual Studio 2019.

The confirm, the solution that worked for me was to follow both Josh's answer and kalmiya's answer:

1. Window -> Close All Documents
2. Window -> Reset Window Layout
3. Press Ctrl + Shift + F, to find some text in your solution
4. Drag the 'Find window' to the bottom-most dock position (see diagram in kalmiya's answer)
5. Restart Visual Studio

If you want to reproduce the problem, simply drag the 'Find window' to the second-from-bottom dock position.

Many thanks for the previous answers!