Password gets changed while proxying

[JB]

Hi!

We're proxying auth requests to another RADIUS service and encounter the following problem:
The password seems to get changed somewhere along the way.
In our case, a 9 character password arrives as 16 character garbage at the home server, which then -of course- rejects the access request.
Unfortunately, we don't have direct access to the home server, but the provider is convinced that the password gets mangled on our side.

I can see the correct password in our FreeRADIUS debug logs.
Other than preprocess, there's no module, which theoretically could change the password, before the proxy realm .

My guess is that this is some sort of double encoding problem…
Or maybe that the password doesn't get decoded properly on their side?

Has anyone encountered a similar situation?

Thanks!
JB