I do not have that DVR model. Setting a program to record from the Guide does not produce that same length limit warning for me. My experience has been that the only time I have received that warning is when I am trying to program a manual recording for longer than 6 hours. When this happens, the DVR gives me the 6 hour maximum warning and then prevents me from setting up the recording. The workaround is to then set up 2 manual recordings to cover the same time period, or go to the Guide and set all the individual shows listed within that time period to record separately.
But this warning prevents me from setting up the recording in the first place. You are saying that it let you set the recording, then limited how long the recording lasted. That is very strange. I live in a 1.9.1, build 14.47 area. Hope that this isn't another software glitch coming in one of the updates.