I couldn't tell you, I'm afraid - my experience above is as of the current patch, a new save started since then.
I didn't talk to Wyll to get that freebie - the very first time I used the tadopole was when entering blighted village, and immediately got the trigger. I rested, the dream triggered, and then I went to the windmill, used it again, triggered another response, and then immediately rested for the second dream. Oh! Wait! No I think I DID use it one other time! With the dying true soul and his followers - so yes, that would mean that it triggered on my second use, and then on my third for the second dream.
It sounds like you may have hit a bug that tripped up the script, perhaps. See if you can recreate it and do a report.
