Thank you both for your suggestions! I meant to respond sooner, but there was a power outage.
In any case, Coises’ original suggestion worked! Thank you so much! I already knew that I had to disable GenericTabNavigationHandler, so all I did was go into the Designer.cs files for all of my forms and rearrange the order in which they were added to their parent and it just worked.
Hand-editing Designer.cs files is kind of a no-no, because they’re automatically generated by Visual Studio when you edit a form in the designer, but I’ll happily take this solution over whatever lousy alternative I was going to use.