Steps to reproduce:

1. Create a new Product Type and save.
2. Edit this newly created Product Type and add one fieldtype, click on the "X" on the left.
3. Create a new Administrator user and log in as him.
4. Try to edit the Product Type from step 2.

Result:
One is presented with an exception:

Could not find 'The Content Type is owned by someone else' with identifier '51'

Expected result:
A pretty notification should be created, just like it's done in Content Types.