Strange warning: Ampersand is case-sensitive. you might have meant that the following are equal

[stefjoosten]

What happened

I got the following warning from the Ampersand compiler vs. Ampersand-v4.7.1:

Unknown origin warning: 
  Ampersand is case-sensitive. you might have meant that the following are equal:
      Relation `Aanvrager` and `aanvrager`.

The parser keeps Aanvrager and aanvrager apart in my source code, because Aanvrager is a concept identifier and aanvrager is a relation identifier. I got no parser errors, so the ADL code is fine. I traced the problem to a .xlsx-file. It contains the following data: It is relevant to know that the source code defines

CLASSIFY Aanvrager ISA Persoon

The second column contains the concept set of Aanvrager. If I remove this column, the warning goes away. So, the identifier Aanvrager from cell B1 is mistakenly added to the set of relations, which results in the shown warning.

What I expected

I did not expect this warning, since everything is fine.