For example its joining them in random order, it ignores how you have them sorted ... but that is minor problem.
I tested it somewhat, and it seems this behaviour is intended, and not a bug:
When you split the group and then join it back, the currently selected character goes to position 1 (becomes the party leader);
When you split the group the second time after that and join it again, this time having the previous party leader selected, the game seems to be remembering the initial party order (that you had before the first split) and restores it.
It appears they put some effort into its implementation, since it behaves consistently. However, as with most LTC-related changes that Larian makes, it feels like another layer of epicycles added to the Ptolemaic system: an awkward and unwieldy crutch to help a bird walk, even though it was supposed to fly instead.
I feel practically sorry for Larian devs, it looks like they are going to get rid of LTC eventually, but because of the enormous internal friction they have to do it the hard way.
P.S. Just in case, +1 to the thread's original idea and purpose.
