When using trueview, if you click on the group, and then click on Axes, it will modify the pivot point of the group. For a rotating turret, you need to set that, and the pivot point of the barrels (also the group). You don't really need lights for the groups, I usually only add lights when there is nothing else in the group and therefore I can't make a group without a light. PCS works without lights, but Modelview doesn't, it seems to use the lights exclusively for determining the pivot point.
Now that you mention it, I remember an annoying error in TS, something like you described. I opened TS and a primitive turret, and I could manipulate every pivot point, so it can't be that, but I don't know how it will (won't) work when converted.