Using OUT on multiple radial tanks causes them to empty unevenly and eventually unbalance the craft to the point of controlloss.

Multiple INs aren't as bad but still cause some unevenitiy.

Edit: my suggested fix didn't work so I'm trying something else now.

Should be fixed by now. There might still be an issue because it starts transferring as soon as you click it, so you cannot synchronize transferring to/from multiple tanks. I usually transfer the opposite direction in those cases: i.e. instead of transferring out from two tanks, transfer in on the other tank(s).