Thanks for the report. I have raised an issue on our issue tracker (
http://www.vassalengine.org/tracker/sho ... i?id=13826) for this. This used to work, the large drop-down menus had scroll capability. I am aiming to get this fixed for the 3.4.12 release.
In the meantime, you may want to have a look at our version 3.5.0 beta release. Beta release 2 should be out in the next couple of days. The more people that can play with the beta releases, the better Vassal will be.
Regards.