It's probably so that people don't accidentally publish something they intended to DM by tapping the spacebar twice after the command. It'd still imagine it should be allowed from a full keyboard, at least.

Nice idea, but 'internal server error' (per the linked tweet, didn't try it) isn't exactly a good reaction. IF someone thought that this might make sense, the result should not/would not be a 500..

It could be that an internal service is returning an error, which the externally facing server is not handling properly.

yes, absolutely! It has to be this. Plus, a tiny little period is really hard to miss on mobile (where the shortcut you mention applies). it's almost justified.

That's an interesting idea but very speculative.

Allowing multiple spaces makes sense, I suppose, but why support a dot stuck there? Seems like an oversight.

On many mobile keyboards double space turns into '. ' as a quick way to begin a new sentence.

"d. something" is not the only offender. I suspect it's a badly written parser. "m. anything" also breaks. And for fun, without the following word ("something"), the tweet just vanishes with no error at all.

I tried all of the non-space non-alphanumeric characters on my keyboard. Some worked, most caused an error.

d` d~ d$ d% d^ d& d( d) d- d+ d[ d] d{ d} d| d; d' d" d, d< d. d> d/ d?