humbly accepts compliment
I suspect it's caused by users who copy/paste a link from elsewhere, but accidentally select too much text, more specifically an extra space in front of the link. Like this:
Do you see the difference? I don't, and that's exactly why these broken links happen. The insert dialog above produces the following link:
enter link description here
(clicking it won't work, since it's broken; you can check the source code of this post and it'll show you that it's
Can some automated process fix the remaining ones?
I've been toying with this for a while. It's possible to search for
url:%20http to find (most of) these posts; that's how I found the example you mentioned. I've written a userscript (maybe I'll publish it someday, right now it's a bit of a mess) which checks posts I'm editing for broken links of this type and tries to fix them. Also, a variation of the Broken Image Repairer is running on the non-English Stack Overflow sites, fixing those links (here are some examples).
The main problem with automated processes is that sometimes the links are broken anyway, even if they had been inserted correctly, and I try to improve other things (grammar/spelling, converting HTTP links to HTTPS) while I'm bumping the post.
Oh, while we're in compliment mode: the user who (probably unknowingly) inspired my crusade against broken links is @Pang, after I saw a couple of their edits across the network.