> The problem occurs when using Firebird Embedded, even with the 2.5.1
> version (it started to happen after upgrading from 2.1 to 2.5
> version). I'm going to put some stuff together and open the ticket

You might want to try the Jaybird version from HEAD (you have to build
java stuff yourself, the JNI libraries are already in binary form
there). There were API change in the Firebird 2.5.x compared to 2.1.x
version. This should not have any influence (we lookup entrypoints by
their symbolic names), but it is worth trying new JNI version - some
parts of it were reworked.

Roman