Hi
This should not happen if you have configured it as per documentation and workflows are working fine
have you checked this link
http://help.sap.com/saphelp_smehp1/helpdata/en/65/37c54b251011d5b3760050dade3beb/frameset.htm
also check below notes
Note 1327409 - Sequence workflow: System cannot achieve status Next Tester
Note 1313997 - Incorrect sequence for test sequences
Note 1872527 - Wrong sequence of Assigned Test Cases in Tester Worklist
Note 1854310 - Link in notification 'Next Sequence Tester' not working
hope above helps if not let us know we try to help further
Regards
Prakhar