When using Lesser Planar Binding with a Tanar'ri summoning theme it summoned a succubus. Not a more powerful succubus, but the same succubus as a third circle Summon Monster spell two spell levels below it. Character sheet and health all looked to be identical, and it got cut down about the same as well.
This is not a bug. LPB summons whatever you would get two circles below except with 24 hour duration.