WinForms does not scale sizes correctly when changing DPI (even for simple controls)

Question

I cannot get WinForms to properly scale the UI when the DPI setting is changed: different controls are scaled by a different factor, messing up the UI design.

This is what I’ve tried:

• In Windows 7 set the text size to 100% (= 96 dpi).
• Start Visual Studio 16.9.1 and create a new WinForms app with C# and .NET 5.0
• Add a simple text box and a button to the form
• Compile the project
• Run the program: both controls have a height of 23 pixels (checked visually and programmatically)
• Set the OS text size to 150% (= 144 dpi) and log out and in again to apply the changes
• Run the program again: now the text box has a height of 31 pixels and the button has a height of 38 pixels.

So when increasing the OS text size (= DPI) by 50%:

• the height of the text box increases by 33%
• the height of the button increases by 67%

Notes:

• I checked all guidelines described here: How to write WinForms code that auto-scales to system font and dpi settings?. The application is DPI-aware and AutoScaleMore and AutoScaleDimensions are set correctly (default values in .NET 5.0).
• I also tried this with .NET 4.7.2 and Windowds 10, but the two controls always scaled differently.

Why are these controls scaled differently? Why are they not scaled by 50% as you would expect? What can I do to have these two controls scaled by the same factor?