I think this has come up here before. (I recall being frustrated by this myself.) I don’t think the issue can be solved.
I’ll try to find the post.
No I guess this was something else I was thinking of. Maybe subreports? I thought there was some element that does this and can’t be fixed per Microsoft, no? A consultant modified our AR Invoice form and I thought he hit that wall, too.
Anyway, Tablixes can be tamed, but I don’t know about textboxes:
This guy is pretty smart… 
Last edit and I’m done. I found it in my notes; it was a subreport. It was really odd; the rows, which were tall-ish, if there were about 11-20 then the subreport wouldn’t start till page 2, but 51+ worked perfectly (starts on page 1 and continues as expected). I didn’t agonize over finding the magic cutoff number and I imagine it would depend on the row height anyway.
I can’t find where anyone else on planet earth has encountered this. Supposedly it was all fixed by or after SSRS 2008, but I’m sure we have always been more modern than that…
And now I can’t duplicate it. Guess I am crazy. 