Mobile Equipment as Covered Property

Our insured is a church that owns a riding lawnmower, valued at $3500. The custodian takes the mower home with him on his pickup after using it at the church. Because of local code, the mower cannot be stored in an occupied building. The custodian loaded the tractor on his pickup to bring back to the church, but in pulling out of his property a low-hanging power line caught the mower and pulled it off the pickup. It was damaged when it hit the ground. The carrier is denying the claim based on the mower's being "mobile equipment."

Frankly, it just doesn't seem that the definition should be applied to something like a riding mower used to service the church premises. What is your take on this?