Steps to reproduce:

1. Create and save item with one preprocessing step, for example with type "Discard unchanged"
2. Edit item
3. Open preprocessing tab
4. Open the existing preprocessing dropdown and close (this is an important step!)
5. Add new prepossessing step, for example with type "Trim"
6. Change the order of the steps. Move the second step to the first
   

Result:
Prepossessing type of existent step was changed. There may be different errors when trying to save item, depending on prepossessing types selected
Expected:
Prepossessing type not changed