Wait, Tap-a-talk does not have a rich text editor? WTF?
Rich formatting is, by default, only used when replying to HTML messages, this is the "automatic" option in app settings, under Composing and Sending, but it's possible to set rich formatting as the default for all, including new, messages.
There was also a bug where formatting could "spill" from a styled signature over quoted plain text (when replying or forwarding). Fixed in 1.2.5.5.
Closing tag getting lost or ignored? I have updated to 1.2.5.5 and have never seen this anyway.
No styling in tapatalk? No, as far as I know, it has none. Just essential stuff like quote and /quote, links, and I know images can be put in, but styling of text, no.
On another board I use, re-editing of posts is allowed within a few minutes of the original time of posting, (but it is not allowed on your board). If you 'quote' a post, as I have done here, but then realise a mistake and re-edit, the quote styling but not the text vanishes totally as you start the re-edit. You then have to hand-code the quote and /quote tags! Nostalgia time.
Back to aquamail. I did a couple of tests and I think the guy who was bothered by the lack of styling in a reply may have been worried that you cannot highlight a word in the quoted text and then bold/underline/italicise it, as indeed you cannot.
You can however style your own reply outside the quoted text.
Styling part of a quote may be useful if your reply is pointing out something about those particular words.
However, I do appreciate you are not trying to recreate a full blown word processor. That way lies madness!