While altering the partition, does the old partition move to new file group?

I have created partition on a table last year using the below script. CREATE PARTITION FUNCTION PF_Table1(NUMERIC(18,0)) AS RANGE LEFT FOR VALUES(100000000); CREATE PARTITION SCHEME PS_PO_Transaction AS PARTITION PF_PO_Transaction TO ([PRIMARY],[PartitionFG1]) I created a new partition this year by altering the existing Schema and Function as below. ALTER PARTITION SCHEME PS_Table1 NEXT USED [PartitionFG2] ALTER PARTITION FUNCTION PF_Table1() SPLIT RANGE (200000000) The Range used is the Primary Key value of the table. Still my table Primary Key value didn't reached 200000000. So basically i am creating an empty new partition. But it took 2 hours and log file size increased by 250 GB. The thing i noticed is my old partition (2nd) moved to new file group (PartitionFG2). And when i inserted rows with Primary Key value more than 200000000, the rows got inserted in partition 3 but its file group says PartitionFG1. I couldn't figure out why the old partition moved to new file group and the new partition data created in old file group. Did i missed anything in the query? Please help me to figure out the problem.