I suspect that, somewhere along the upgrade path, I didn't properly u prompts file, but it could be something else.
You are correct, you need to find the prompt and update it, the correct prompt is:
Message base "To" input default value
Prompt: 104/554
Thanks so much for this; that was an easy fix. You know it's funny -- it has probably been years since I've used the prompt editor and it seems ridiculously obvious now that I've fixed that. Thanks for the pointer; working properly now.
--- Mystic BBS v1.12 A48 (Linux/64)
* Origin: Shipwrecks & Shibboleths [San Francisco, CA - USA] (21:1/227)