Wow, i didn't even know that projection is working in Corona at all! I could use it couple weeks ago. Although it seems from my quick tests, that it still has quite a few problems.
So I found a work around, set up projection as usual, disable all rendering the low poly object, then turn projection off in R2T menu (keep the projection modifier on low obj however).
It kinda works, but it gives completely wrong padding, not usable in most situations. I would suggest to save bake with alpha and do the padding in photoshop - there is free photoshop plugin from Flaming Pear - Solidify, which makes excellent padding in one click.
The main reason is that whole RTT is an ancient, badly documented feature of 3ds Max.
It might be ancient and somewhat awkward to use, but it's the only tool that can bake Corona lighting onto models and that's quite important feature to have. Please don't abandon idea to fully support projection baking with Corona sometime in the future! The sooner the better ;]
