> AFAICT, there is a performance bug here in that just doing the
> `C-h o PREF TAB` which completes to `PREFIX-` already loads `PREFIX.el`
> which is a bit over-enthusiatic (I intended it to load `PREFIX.el`
> only when you hit TAB while you already have `PREFIX-` in your
> minibuffer).

The patch below seems to fix this performance bug in my test.
Can you see if it avoids the major slowdown you're experiencing?


        Stefan