are all files for an sstable immutable?

[Sean Bridges]

Hello,

I thought an sstable was immutable once written to disk.  Before upgrading
from 1.2.18 to 2.0.10 we took a snapshot of our sstables.  Now when I
compare the files in the snaphot dir and the original files, the Summary.db
files have a newer modified date, and the file sizes have changed.

Thanks,

Sean