I suspect this is a "feature" rather than a bug so to speak, but when I post a URL on a phone as BB Code, ie (But without the spaces):

[ url= www.website.com ] the text I want to appear [ /url]

it's like it sees the URL part as what I want the text to be, so it turns that into a clickable link, with nested BB Code tags. So you get something like:

[url = ][url = www.website.com] www.website.com]]the text that I want to appear[ / url] [ /url]

It's fine when I post on a PC. But I always have to go in an edit a post on mobile to delete all the superfluous text and get it to display properly.