[NTG-context] odd end-of-line error w/ Minion Pro

Hi, I'm seeing a strange behavior with Minion Pro in OTF and the simplefont package. I'm not sure if it only happens with simplefont because I don't know how to set up a typescript. In any case, in breaking a line between roman and italic text, ConTeXt is losing a bit of space at the end of line. I thought it might be related to using hz or hanging alignment, or the quality option for protrusion and expansion, but it seems to happen even with these features disabled. Very unclear what could be causing this. Is it a known issue? What is this kind of bad behavior called? I've attached an image to which I've added a red line to show where the 'a' is leaving extra space before the newline. Thanks again, — Daniel Lyons