I'll pass it on, thank you!

Was it an Alliance planet, a neutral or unknown planet? Did it have a base on it (i.e., was it a Krellan planet)? Which version of the game are you playing? This could be a problem before 2.0.15, but was "fixed" for the latest version.

Neutral planet (in UGA space - I am on mission A-3 where you have to build bases in systems with UGA presence).

It did not have a base on it, I was in the process of building one. I am playing on the latest version.

I did manage to replicate the bug I think.
Step 1: Land teams on planet
Step 2: Add a team to one of the tasks
Step 3: Try and beam up the team on the task
Step 4: Beaming up multiplies the crew (possibly by 5 times)

From then on that planet you can beam down a team and get that team + and extra 5 back.

I think straight beaming up/down everything on the planet is fine (as I earlier in the mission I pulled all my teams off a planet with Alliance troops on it), its when you try and add a few teams extra to speed up a task and then pull them back it seems a bit dodgy.

Thanks. I'll check it out.

I tried doing your steps and it worked fine. I got the 10 members of my LP back. Here is what I did. I beamed down 3 Survey teams and 3 Establish Base teams initially. Arrived safely. I then selected Landing Parties and said "N" to when it asked if I wanted to beam any teams up. I added 1 team to Survey mission. It beamed down fine. I then called up LP command again and this time I answered "Y" to if I wanted to beam any teams up. In the table I reduced the "4" Survey teams to "3" and pressed [Enter]. It returned the 10 members of that one team.

I've run into the same issue. On mission A-3:

I had beamed 10 survey teams down to a world that ended up being alliance and retrived them so I had 272 Crew and 150 shock troops.

Left that world and went to another system and found a tech lvl 4 neutral world.

1) Beamed down 10 Survey and 10 Base building teams
2) activated teleporters again and said don't beam up teams
3) added 5 resupply teams
4) waited till all missions had been completed
5) beamed teams back up
6) all teams returned but I now have 379 crew and 240 shock troopers.

I believe this has been fixed. I'm on travel and don't have access to my notebook.

I have the same problem, I sent 5 survey teams to a planet, when I sent them back I got 340 crew members.