I have a race in my world that has the ability to transform into animals at will. For reasons of practicality, the animals do not wear clothes and the clothes disappear during transformation. For reasons of public decency, when the race transforms back into humans, they are still wearing the clothes they first transformed into.

Now, in order to prevent this race from having the ability to carry an infinite amount of items, only garments transform with the person. Things held or purses do not, and end up below or on the animal upon transformation. Why would this occur?

Notes: 

* Ideally, items in pockets would not transform, but that seems to be a stretch, so you can drop that caveat.
* Deities do not factor into the magic for this world and cannot be used.
* The transformation does not necessarily follow this world's laws of physics, but I do want the reason for transformation to be reasonably logical and consistent.