Understand - - and thanks for asking your intro-to-TB questions, which I find an instructive process for people at every stage of using the program.
I haven’t run into the other UI issues you mention, so I’ll leave them to the technical experts here. I’ll amiably suggest that this particular pattern you’ve found is less an illustration of something amiss than, probably, of an edge-case scenario no one had exactly imagined before. (“What if we go immediately to Full Screen view before putting any data in a file; and what if our very first item in the file is by clicking on the map; does anything unusual happen to the splitter then?”)
I don’t know whether it has any bearing on the other issues you raise, but my guess is that in itself it illustrates an unforeseen use case rather than a bug in the usual sense.