A Wizard and a Knight clad in chainmail are happily walking through a forest. A wily Druid pops out of a tree and casts Heat Metal upon the Knight and he begins melting in his armor, screaming.
Rolling well on his Initiative, the Wizard decides to Polymorph the knight, who is very willing, to try and save him from a horrible, fiery death.
Heat Metal damages via physical contact:
Any creature in physical contact with the object takes 2d8 fire damage when you cast the spell.
Polymorph "melds" objects into the creature and common sense dictates that the object is gone. However, Polymorph is curiously worded:
The target's gear melds into the new form. The creature can't activate, use, wield, or otherwise benefit from any of its equipment.
Emphasis mine. Clearly, the description is saying that the user pretty much cannot use the object or be given any benefit, like a magic item. But can the object still be a detriment? After all, it still satisfies Heat Metal's requirement of being physically attached to the creature, and it is clearly not providing any benefit.
However, I can also understand the viewpoint that "the object" may not necessarily be an object anymore - it's part of the new creature. I do find it curious, though, that the stipulation of the creature not being able to benefit from or use the object is written in, rather than saying it simply doesn't exist for the duration.
Is the Knight still afflicted by Heat Metal while under Polymorph? Can the Druid still recast Heat Metal while the Knight is in his new form?