SAP Note 22708 - Foreign key check is incorrect for some data types

Symptom:

The check of foreign key relationships on screens is incorrect.

Cause and prerequisites

Fields were used for the foreign key, that are not character-like types such as INT1, INT2, INT4, DEC.

Solution
In the foreign key check on screens, only character-like data types can be used. If checks are needed on the user interface, you should use the Dictionary type NUMC for numeric data types.