Fleets do disband when the go into orbit - that seems to be the intention. If build an orbital fleet manager ships in orbit will defend as fleets based on your logistics (but I digress).

There have been other posts about the issue with selecting and moving ships and the associated "wonky" behavior (just saw that word in another post and had to use it).

I can usually get around this issue IF I notice that I have multiple ships selected. Sometimes I'll have ships multiselected from two entirely different stacks - and I have no idea how I did it. I have to click around and do tricks til one and only one are selected, then move it. Even so, sometimes it seems as if sometimes I have other ships selected and the selection isn't showing on the screen and I end up moving multiple ships at once. No clue how this happens. For example, I might've been moving around some transports that were in a stack but never grouped. Then I select a warship to move. Somehow all the transports, even though I saw no indication of them being selected, will move to the same place I send the warship. It's brutal.