You have an af:query with an View Criteria attribute that has a LOV.
If this LOV has only 1 row then it will return automatically the value of that row to the View Criteria attr.
This is regardless of the VC attr being required or not.
So even if you go and erase the value, when you select the next field, the LOV will populate it automatically.
There is no any. This is default ADF behavior (?!?)
If user want to clear the VC attr of the af:query must click Reset.