We have a problem with three of our 6408D+ sets (total of nine on system). When pressing SPKR to activate speakerphone, these sets go into 1-way mode (the MUTE goes active with the SPKR). I've tried unpluging the sets with no change. The STATION settings clearly have the correct Type:6408D+, Speakerphone:2-way, and Mute Button Enabled?y settings. I swaped a problem 6408D+ with a non-problem 6408D+, and the problem followed the set. In every other regard, the sets operate perfectly. This problem surfaced about a month ago with all three sets, simultaneously. Even though it looks like the set has the problem, I'm not convinced.... Any similar experiences out there?