The space following a single char always gets stripped.

Use quotes

Thanks this issue has been fixed for the next version.

It looks like it's no longer possible to launch programs with parameters using /run, perhaps related to this fix?

These both work fine.
/run "cmd" /k dir
/run cmd.exe /k dir.

Interesting, thanks. It looks like the only syntax that fails is this:

/run cmd /k dir

which worked fine in previous versions.

If the formatting is ambiguous, eg. uses a path, command and parameters that contain spaces, the /run command has to guess which is which and split the line accordingly. The recent fix seems to have resulted in a stricter parsing method. I will see if I can revert this while maintaining the current fix.