When an I-485 is accepted at the Service Center, requests for FD-258 FBI fingerprint checks, fingerprint fees, and G-325A consular background checks are made by USCIS. Responses to these requests come back to USCIS and must be matched up with the appropriate files held in staging. File Maintenance "file connects" these responses to the corresponding files.
USCIS recently began transferring some Form I-130, Petition for Alien Relative, cases filed by lawful permanent residents for their eligible family members from the Vermont Service Center to the California Service Center.
If your case was transferred, USCIS will send you a notice listing the transfer date and where your case will be processed. Your original receipt number will not change and this will not delay the processing of your cases except for the additional time needed to transfer the file.