extensions classpath?

I have 2 groovy scripts, one which needs a sybase driver jconn4.jar, and the other needs a custom jar, which itself needs the jconn4.jar.

When I put both in soapui's lib folder, both work. But I don't know if this is the intention. Because in the documentation I read that the bin\ext folder is meant for this. 

When I put jconn4.jar in bin\ext instead, and run soapui.bat, I see:

14:14:52,571 INFO [SoapUI] Adding [D:\dev\SoapUI-5.4.0\bin\ext\jconn4.jar] to extensions classpath

But when I run the first groovy script,  in this case, I see: No suitable driver found for ...

So what does extensions classpath mean?