A new branch for the fix has been created and a test was committed:
https://github.com/aerogear/aerogear-unifiedpush-server/tree/1.0.0.Beta1_fix

Updated test, that triggers the failure:
https://github.com/aerogear/aerogear-unifiedpush-server/commit/c48c6f648c343bdeea6b007324174034aa8ee4c6

I tested on the 0.11.0 tag. Applying the commit there does not cause the constraint violation there.