Interesting!
I've considered wax or any thing else that would keep a fill (resin, epoxy, filler) from sticking to the outer areas, but never thought about the aquacoat. It'll still stick, but with a layer of sandable between the fill and wood that doesn't need to be completely eradicated, Bob may indeed be a relative.
I do like that it can be applied to raw wood, then a followup with a finish like oil will still look the same, as if the AC was not there.
So you just buttered it up to fill the pores, etched the image, filled, and results was the TM didn't invade the off limit pores?
May have to try that with some resin/epoxy as that is where I use tape the most. Masking tape works well as a barrier, but yes, it can be an issue to remove unless preserving the surface from heavy sanding doesn't matter.
With the tape and using a water based filler for the etch, the sanding is super easy so the tape can be peeled off easily (still have the "O" issues).