A learning remote has to learn a button correctly (as one keypress) no matter how long you hold it down (since you can't control that to the microsecond). So it will always correctly learn just one Press of the button. If it learns it as repeating, that's a bug.

Given this, it's not clear that the remote would be designed to allow it to send a repeating code, since it can never learn one in the first place.

You do know that a repeating code is not just repeated copies of a single press? If not, refer to some of the documentation on IR codes found in the files section of Remote Central for the older Pronto.
Barry