A recent email from USCIS: From January 5 through March 28, USCIS began sending some cases between service centers in order to balance workloads. We have updated our Workload Transfer Updates page with this information:

• Some Forms I-765, Application for Employment Authorization, for F, M, and J nonimmigrants went from the California Service Center (CSC), the Nebraska Service Center (NSC) and the Texas Service Center (TSC) to the Potomac Service Center (PSC).
• Some Forms I-539, Application to Extend/Change Nonimmigrant Status, for F, M, J, or B nonimmigrants went from the VSC to the CSC
• Some Forms I-129, Petition for a Nonimmigrant Worker, for petitioners requesting H-1B nonimmigrant classification went from the VSC to the CSC
• Some Forms I-130, Petition for Alien Relative, for immediate relatives went from the NSC to the PSC and the TSC
• Some Forms I-129, Petition for a Nonimmigrant Worker, for petitioners seeking L, O, and P nonimmigrant classification went from the VSC to the CSC (except for major league sports-related P petitions which will remain with the VSC)
• Some Forms I-129S, Nonimmigrant Petition Based on Blanket L Petition, for L nonimmigrant classification when from the VSC to the CSC
• Some Forms I-539, Application to Extend/Change Nonimmigrant Status, for applicants seeking the L-2, O-3, and P-4 nonimmigrant classifications that are filed together with Form I-129 went from the VSC to the CSC (except for major league sports-related P petitions which will remain with the VSC)
• Some Forms I-765, Application for Employment Authorization, for applicants seeking L-2 status went from the VSC to the CSC