I think the issue is that when the saved reply is the same as the originalText, the draft with the change (i.e. with the extra space) is not removed, which causes this composer.open function to be triggered (as the draft is not empty) when the topic-from-params route is loaded again.
This is an educated guess though, as I wasn’t quite able to track down (or, at least, understand) the exact source of the ‘draft’ appearing in topic-from-params route in this scenario.
If I’m correct, I would suggest this is technically a bug, albeit a minor one. Having the composer reopen on refresh after saving an edit with no changes is probably not expected behavior. Of course, triggering a draft to be saved, and then not making any changes when actually saving the edit would be rare.
It is a bit more relevant if you’re adding extra content to a post, like in the Topic Ratings Plugin, as the likelihood in which posts will be edited without changing the reply itself increases. Given this, I’ve tried to get to the bottom of the issue, but haven’t had much luck so far. I’m going to give it another shot soon, but thought I’d file this in the meantime.