1) I’m assuming you did the masks and Write on to the text layer.
It’s because the Write-on defaults to comp size layer, I think. The text layer, or whatever layer you reveal needs to be the same size as the comp, otherwise you get an offset difference. At least I think that’s what’s going on.
Right after you create the text, precompose it (Layer>precompose, open comp) and you’ll see the precomp is the same size as the comp) now, on that precomp text layer, if you do your Mask, copy Mask Shape and Paste into Brush Position, it’ll work.
Jayse uses Write-On here, but the layers are the same size:
https://library.creativecow.net/articles/hansen_jaysen/growing.php
2) I just use Render>Stroke (set to Reveal Original Image). It does the same thing, but doesn’t have the offset problem, and you don’t need to precomp the text layer, so just do the masks and Stroke to the text layer, it will work as you expect.
Andrew does Stroke here:
https://www.videocopilot.net/tutorials.html?id=25