<ahem... hangs head in shame>
So, it would appear that my Android keyboard occasionally adds a space after a period when entering an IP address... I didn't notice until I saw it happen on the much larger screen of my tablet in pinger (i'd changed the keyboard on the tablet to match that on my phone after I installed MMC), but lo and behold, when I checked on my cell phone, there it was - a little space lurking there.
I'll be in the corner feeling stupid if anyone wants me!
I do, by the way, love this software. It's exactly the sort of thing I was looking for to control my media center. When I've recovered sufficiently from my shame I will mention one other problem I'm having (though I suspect it's very much due to the particulars of my set-up), but for now I'll slink off and enjoy your work!