It also doesn't show up, because you put a spaces between the link and the [IMG] tags. (EDIT: hmm, it still doesn't always show up... logic is here. ) If you say this number, 15115, like how I sometimes remember the number to go look it up, "vijftien honderdvijftien", you also get 1515 (vijftienhonderd vijftien). Interesting!
(with a bunch of spaces after the [IMG] tag. ) Edit: They got removed now though, which was expected. Apparently the single space doesn't get removed, though, which could also be expected. In any case, my point is that it doesn't matter. There is always a space after the tag when I post from my iPad.
Because on iOS, a shortcut/text replacement isn't activated until you press space. I use shortcuts for the tags I use often on mobile, so I don't need to go to the sign keyboard to get the brackets, and because I like to write the tags in all caps, and that is not as easy on mobile.