There have been often reports of wrong slider positions with new versions, but we could never confirm them. 4000 is the default capital of Z12, so when you start it, it indeed jumps to 4000. But once you set it to a different value in live trading, it keeps its position, and if you stop and restart the session, it should resume its previous position. Please try.
If you trade several Z12 in parallel, without the described precautions, they will share all their logs, trades, slider positions and other data, and this can of course cause strange behavior because the script is not made for such a configuration.