Dock Problems

How come when i remove something from the dock or I put something there (both by right clicking on the icon), whenever i reset whatever I did gets erased. Is there a way to fix that. I tried checking the pref. and that didnt shed any light.
Thank you in advance for any responses.

That should only happen on forced (hard) restarts, when things don't have time to save properly. Are you restarting as normal?

I think this happens even on a normal reset.

When you put an item in the dock, do you ctrl+click/right click the icon and click "Keep item in dock" ?

are you putting items from a disk image in to the dock?