Exactly as i found tomcat.
Think about it this way. You've defined a region and changed some automatable setting (forget the fact that you just commanded protools to do a glide). Once you hit play the primed setting is written over the glide you just made.
If you were to turn off the latch prime pref, or be in read automation mode you would see that glide works perfectly.
It's not quite a bug, but it would be convenient if the Glide command over-rode Latch prime.
Here's my original take on this.