I haven't installed this version of MIUI yet, but on 1.12.30 (I think that's the version right before this one), I have no trouble answering calls. It might lag for a couple seconds before the answer screen pops up, but my phone doesn't completely freeze like it did on Liquid and CM7.
But right after I installed MIUI, before I could test for the phone calling bug, metalspring suggested that I
unroot my phone and flash to the stock ROM with Motorola's sbf. Then, after I did this, I rooted and flashed MIUI again.
So I don't know if the bug was fixed when I installed MIUI or when I unrooted my phone. I'd say that if you're going to install a new ROM, you might as well try running the sbf (if you have Windows, that is; I don't know how to do it on Linux or Mac).