[rdiff-backup-users] how to shrink/purge/truncate the metadata file (and the file_statistics file)?

[=JeffH]

My rdiff-backup-data/mirror_metadata.*.snapshot.gz file seems to grow without 
bound, even though I have perodically used --remove-older-than to remove a 
number of prior increments. I.e. I expected --remove-older-than to 
shrink/purge/truncate the metadata file (as well as the file_statistics file), 
but this seems to not be the case. So eventually my backup disk fills up.

Is there any way to get rdiff-backup to automagically shrink/purge/truncate 
those files, e.g. when employing --remove-older-than ?

If not, the only way I know to address the issue is to delete everything on my 
backup disk when it gets near full, and the start all over with an effectively 
full initial backup. This seems suboptimal for various reasons.

I'm using rdiff-backup 1.1.5

thanks for any insight/help folks may be able to offer.

=JeffH