Sharing Records - unexpected behaviour

When a user shares a record with another user the sharing user specifies the permissions to share.

Consider this scenario:

a) User A is a member of one role only that gives him None - Delete access and Organization Level Read and Create Access on Accounts.

b) User B is a member of one role only that gives him User Level Delete access and Organization Level Read and Create access on Accounts.

c) User A may create and view accounts but not delete any and User B may create and view accounts but only delete the ones that he owns.

d) User A owns an Account, "ABC". Neither User A nor User B can delete the ABC record but both users can view the account.

e)User A shares the account with User B and grants Read, Write and Delete.

f) The CRM application will allow User B to delete the account, "ABC".

User A and User B have been able to acheive an outcome that neither of them could achieve separately. Although this may seem wrong, it is in accordance with the CRM security and sharing model.