The BTO folks are using an RO relation "part of" without declaring it transitive:
BRENDA-Enzymes/BTO#43
This means that anyone who is using OWL reasoning will get mysteriously incomplete examples (people who use pre OWL graph walking are immune to the problem).
There is no indication of this problem here:

I think both BTO folks and users of BTO would welcome the ability to spot these kinds of issues ahead of time, and I am sure this applies to many ontologies too.