Moving units around inside of a stack

I've been playing vanilla MTW for a few months now; I've started being good at using group formations in battles, I've got my trade up and running but one thing I still don't know how to do, it's so darn un-intuitive:

how do I change position of the unit I have selected inside of an army on the strategic map? I try to drag and drop them on the new position at the bottom of the screen where the composition of the army is displayed but it just drops back to where it originally was, like it was glued to the place or something... IS there a way to do this?

Anyway, although the game is really great and requires a lot of brainpower to defeat which I enjoy thoroughly, I'm finding more and more that it's full of small quirks like these, things that could have been done in a lot more logical manner, if only they spent more time testing it and applied some common sense in designing the strategic interface...

Hope they finally do away with these glitches in MTW 2 - if I would be given a chance to change only 1 thing in the new game, it would be the abillity to stack special agents, to never again have to spend about half an hour of my total campaign playing time in a given campaign just moving the 10 or so of my agents (inside of a "task group") around one by one... who implemented that in the game design must have been smoking some heavy stuff at the time...

You have to take the unit out of the original army - highlight the army, select the inidividual unit and place it anywhere in the same province. The men give a little roar and the unit separates. If you've moved the original army you have to bring the unit out in the original (pre-moved) province or it will indeed just pop back as you've experienced.

Did I understand you correctly?

I don't know of any way to rearrange them as you'd like to. If you remove them from the stack as Matty suggested and then drop them back in it'll usually put them right at the front, but that's an awkward and time consuming way to go about it, and then it'll probably auto-rearrange them for you by the next turn or so anyway. Army organization in general is a little quirky and frustrating, but the game has plenty more good qualities to balance it out.

Ajax

If you highlight a province, not just a stack, and press the "m" key it will merge the various units in the various stacks into one or more stacks, and it will sort the units when it does this. It's a little funky, though - if you have more men than will fit in one stack then it makes two (or more), and tries to distribute the unit types evenly between them. You can manipulate what gets combined by moving units/stacks you don't want to merge into the castle or an adjacent province before you hit the "m" key.

(I don't know if it makes a difference, but I always play with "auto-tidy" turned off.)