Sorry I didn't respond after I tested the other day. Many loose threads on this one....
True. Have they ever? I only checked 24.6.1. I tested in 25.1.0, and maybe Beta 25.2.0.126.
If it doesn't work, it should not offer the option. I suppose even if you can't rejoin/uncut, having the through edit indicator is useful. I assume they did not provide this functionality because the caption track is a different creature, and caption segments are independent items.
You can undo caption segment cuts, so they could program a rejoin. Cutting a caption is a "split," and creates two independent caption segments. The new timecodes respect the playhead position, but each has the identical content/text. Unlike joining a through edit, merging adjacent caption segments uses the beginning timecode of the first and the ending timecode of the second, but combines the content from both. So not an option for the rejoining a through edit.
I realize that I avoid this by adjusting captions so I do not cut in the middle of one. I tend to edit the transcript, even when I am using captions to track the text while editing. But I don't really care how the captions display or cut cut up, because I'm going to regenerate the captions when the edit is done.
Thanks Stan, it's not a problem, but they probably should get rid of the context menu option if it's not going to work. You can delete one and stretch out the other.