Your tooltip DID show acid damage in your PoT3 version, so it was definitely screwing with your conversions.
Korsar made a super useful image detailing the order of conversion, but it got lost when things got ported over to the new forum.
Conversion on Equipment and Buffs > Equipment, Auras and Passives...what does it actually mean?
This was the post where the vets clarified a lot of my questions. Might be useful.
EDIT: found the image - https://images.vfl.ru/ii/1525283771/ededce19/21590161.png
2nd edit: As a frame of reference, this is the order of conversion as listed by the official game site -
The order of events for Conversion is as follows: Base Skill > Skill Modifiers > Conversion on the Skill or Transmuter > Conversion on Equipment and Buffs > Equipment, Auras and Passives