In reply to this, user GothamNY replied, "Haha, let's get the primary function working before we worry about collapsing the folders. This hasn't sorted a bookmark in almost a year for me." Unfortunately I fumbled my phone while moderating the new messages and hit "reject". I didn't mean to do this and I'm not trying to hide critical messages! Sorry, GothamNY. If you wanted to resubmit I'd try not to refumble, but I can't find a way to retrieve accidentally rejected messages here.
My response to the original question would agree with GothamNY: I need to focus on core features for now and evidently some people are experiencing bugs. But I will add the suggestion to my list and return to it when core features are taken care of.
And GothamNY, I'm sorry you're experiencing problems. Version 0.5.4 should fix a couple of bugs (released just over a week ago) and the next version (coming soon) will fix some more. The upcoming version will also improve duplicate identification and removal, adding a couple of much-requested options.
Thanks everyone for your feedback,
Richard.