Full backup is much larger than source directory?

Currently my backup drive has one full backup on it.
The total size of backed up files is over 200 GB, but the total size of the source files is about 84G:

pw@slinktopp2 dejadup2 $ du -h --total duplicity-full.20111219* | tail -n1
202G total

The source directory for this backup is my home directory, which is much smaller than that:

pw@slinktopp2 dejadup2 $ du -h --total ~ | tail -n1
84G total

Why is that? Is that normal, or maybe it suggests something is wrong with my configuration?

FWIW I'm not using duplicity command line, I'm using deja-dup.
I have duplicity 0.6.10-0ubuntu1 and deja-dup 16.1.1-0ubuntu1
I am not using encryption.