Tenser's Floating Shield has the following propertyDDI:
You can use this item as an optional focus for the Tenser’s Floating Disk ritual. When you do, a force bubble over the disk prevents creatures other than you from moving anything on the disk without your express mental permission, and objects gain resist 20 to all damage while on the disk.
I put this item as part of the treasure parcel for last night's climatic encounter - the same encounter one where the mage first decided to use Tenser's Floating Disk as a perch. Now I'm afraid that being used as a mount with Tenser's Circular Disk as a focus will grant her resist 20 to all. What have I wrought?