Hello ,
The issue that you have reported was unrelated to the original issue, however after testing out the reproduction steps that were provided we found that there was an issue. This issue has been reported and will be under further consideration by the developers. The issue occurs specifically with a C++ version of the widget that you made. If you were to remake this widget in blueprints it should work fine. If you are trying to do straight C++ UI elements then extending UWidget , the base widget class, or making something directly in Slate could be a better way to go about it. I hope that this information helps.
Make it a great day