I know this is not a common use case, and you probably don't want to
support it. But I'll open up the e-mail pointing out that I've seen
this exact behavior with local X displays, when they're running slow,
so it would be nice to fix it.
Something on the new SQL editing panel with syntax highlighting is
making it skip key input when it is slow to update. I've noticed it
particularly true on remote X displays (ssh -X -C), which would
indicate it involves communication with the X server.
I would propose a quick way to patch it up, is to delay syntax
highlight processing when input is happening, and only do it when,
say, a timeout without input occurs.
I might be able to work out a patch if given a pointer (where to look
at in the code).