I downloaded an existing RTF Editor custom user control from http://www.workaholic.hu/temp/RTFEditor.zip which I then upgraded to .Net 5.0 following this guide after checking using compatibility analyzer and it works as it did before..
I added that project to my solution and when I view the custom control in the VS Designer window in it's proect everything looks fine, all of the toolstripbuttons have their respective images.
But when I run my own application none of the images show up. I have stepped through the code and it seems to be loading the bitmaps ok, the bitmap property on the following line shows height and width of 16, they just show up wrong.
This is how the images are applied inside InitializeComponent
this.tsOpen.DisplayStyle = System.Windows.Forms.ToolStripItemDisplayStyle.Image;
this.tsOpen.Image = global::Workaholic.RTFEditor.Properties.Resources.open;
Note, Workaholic is their namespace not mine.
The only thing I'm doing that's non-standard is dynamically loading instances of this control at runtime rather than adding it at design time, but the reference to it is statically linked as normal.
InitializeComponent is being called though as expected as I can break in it and inspect that it is indeed loading the images from its Resource file.
In this image, top is how it's displayed when I run my project and bottom is how it displays in the designer.
If I manually add it to the form in my very basic project the display is the exact same in design view as when I run it.