Steps to reproduce:

1. Create 2 hosts with discovery which creates host prototypes with same group prototypes.

Result:
After discovery runs on first host and group prototypes created discovery on second host goes fail with errors like this:

Cannot create group: group with the same name "Server/IBM/9040-MR9" already exists.
Cannot create group: group with the same name "Server/IBM/8408-E8E" already exists.
Cannot create group: group with the same name "Server/IBM/9080-M9S" already exists. 

Expected:
Normal usage of host groups with multiple discovery from different hosts.