We cannot change the Department OBS on the properties page of an investment.
Release : 16.1.1
This happens because once you enter a Department OBS the financial department also gets populated on the financial properties page. These two fields are essentially the same thing.
This is documented here
In the past it was possible to change the department OBS which caused the two departments to get out of sync and creating two entries in the prj_obj_association table for the department obs on the investment.
As a result of this, the financial properties page could not be opened as there was a duplicate.
This issue was fixed in 14.3 by making the department OBS not save when a change is made to it.
The correct way to update the department OBS is to do it on the financial settings page.
This way the two departments stay in Sync and the Location will also need to be reset as that also blanks out when the department is changed.