I also noticed the same problem. Here's a minimal test case that demonstrates the problem:
mkdir -p /tmp/duplicity-test/a cd /tmp/duplicity-test/ touch a/one touch a/two mkdir b
PASSPHRASE=password duplicity --exclude-device-files a/ file:///tmp/duplicity-test/b
I also noticed the same problem. Here's a minimal test case that demonstrates the problem:
mkdir -p /tmp/duplicity- test/a test/
cd /tmp/duplicity-
touch a/one
touch a/two
mkdir b
PASSPHRASE=password duplicity --exclude- device- files a/ file:// /tmp/duplicity- test/b