Example: 

- One LISE instance (A) has a LISE Instance Item fielddef (F) to LISE instance
(B)
- Fielddef F is setup as a dropdown
- Item A.1 has item B.1 selected in fielddef F
- After some time item B.1 is set INactive 
- Now edit Item A.1. Note that the dropdown for fielddef F is set to the first
item in the list. I guess because item B.1 is not available anymore
- Save item A.1 note that the value of fielddef F now has changed for item A.1

I doubt this should be the intended behavior. Items can be inactivated
temporarily for example. Or while preparing an item which is not tp be published
yet. It's kind of unexpected behavior that editing an item from 'A' will get
another value for fielddef 'F'

I can understand why it's happening. Perhaps you can think of a solution (e.g.
allow inactivated items to be selectable).