Undefined index "master_itemname" in item edit form

Create some master and dependent items as follows:
A (master item)
A: B (dependent)
B: C (dependent)
X (master item)
X: Y (dependent)

Update item A and change so that A depends on Y.

We should get an error, which is expected, but we also get unknown item name in multiselect resulting in null and undefined index master_itemname.