The only thing I can tell you is that it doesn't work when switching to c3p0.
Here is the build before c3p0: https://travis-ci.org/Blazebit/blaze-persistence/jobs/76701992
This one here is after configuring c3p0: https://travis-ci.org/Blazebit/blaze-persistence/jobs/76713726
This is the only one commit difference between these two builds which is exactly the c3p0 config: https://github.com/Blazebit/blaze-persistence/commit/75ed755933cb6514b4c4d5a0d61fa104f7742f66