Hi Andy,
Sadly that's how things look for PSP since a very long time. I've come to the same conclusion long time ago, with the exception of reaching the end of its life-cycle. It looks like it can get away with that (in my eyes this must be going on for many years) most probably because it still offers quite a lot for the money. But it seems like its popularity is getting progressively lower each year
The program is full of inconsistencies all over the place, and clear signs of very poor software design/development/programming tactics. It could be any of several reasons, like laziness, too tight deadlines, undermanned dev team, underpaid staff, frequent staff changes, poor to mediocre skills, etc.
There have been so many "wake up" calls for Corel already throughout the years, alas most of them being either ignored, or not being capable of doing what it takes. To me, the most recent such "wake up" call should be Affinity Photo. No one really knew about it, until a few years back when they decided to completely scratch their existing code and started re-building everything from 0. Now they even challenge Ps.
This makes me really sad because PSP could be a major kickass program in its genre today (actually it could have already been since a very long time). It actually was a major player back in the day.