You are right. Let's see if I can fix this. I tried on Windows 7 now and got these issues:
The framerate jumped to 800 fps which is way too much. (with Linux I always get 60-65 fps)
The lags after dropping items on the character appeared too.
The game took a long time to start.
It didn't crash, though.
I updated to the newest lwjgl version, but it didn't change anything.
I will see if limiting the framerate helps.
You are going to the game dev side or what?
I have some games in my mind that I really need to make. So, yes.
However, the last game I posted was for university. This one is for me.
Thanks for feedback to help me find some issues.
Next time I will turn on logging.