Sounds like you had your proper ILS freq and front course dialed in.  You didn't specifically mention hitting APP.  That's what is going to take over and follow the glideslope.  Of course, you can see the glideslope arrow moving down to center and then toward the bottom without actually following it, so that's what was happening.  Glideslope is managed reliably for me, as long as I intercept from below.  I use LOC first, then APP once I'm confident I'm tracking.  Sorry if all this is old news, but hard to guess what went wrong.