I am having this issue, Joomla 2.5.8 and HikaShop Essential 2.0.0
Create any hikashop menu item, click apply, then click HikaShop Options. Make any changes I want, but as soon as I hit save or save and close the settings revert back to the initial settings.
Message at the top says "Successfully Saved".
EDIT:
Assuming the parameters get written to the #__modules table for a given menu item module? there are no parameters in the table. not 100% sure thats where they are supposed to go.
EDIT #2:
It appears that this is an issue with (at least) Firefox. I am able to make changes and save them using IE9.