This bug essentially makes it so that you can't move a location up one rung of the location tree. To illustrate this:
Here is our location parent-child relationship:
Aubry is child to Balmain who is child to Canterbury.
This bug stops a user from changing Aubry's parent to Canterbury and it does this by removing Canterbury from the available list of locations when trying to select a parent location.
This occurs because the system considers Balmain to be Aubry's parent and so removes the option to move Aubry potentially above it. The workaround for this is to:
1) Change the parent location of the affected location to "Select Location"
2) Save the location
3) Attempt to pick the desired parent location again.
This workaround has proven to resolve the issue until the bug is fixed.