[PvK]

It's a feature, but if you don't know how it works, it is a pain. You can hold down the SHIFT key while you select a unit, and it will join or leave a group with any other selected units. This way you can create Groups of units that move together. You just have to know to use SHIFT to remove them when you want them to split up. Also be careful if some of them are stealthy, because they will Sneak when they can, while others who can't will Move, unless you order the group to Move.

PvK