CTD on loading Gondorian large town siege battles

[Lightfall]

Hi all. Can anyone help me out with this CTD? Every time I fight a battle in a Gondor large town (sally out or assault) the game CTDs part-way through loading.

It only seems to affect large towns - I've tested towns and cities with no problems - and doesn't seem to affect other cultures either.

The error log is no help - the last entries before the dreaded 'unspecified error' are to do with banners, and I'm pretty sure there are no problems with those.

Any help appreciated - I can't keep autoresolving forever!

[Lightfall]

Correction: after further investigation, it turns out I've got the same problem with Dwarven large towns.

This suggests the problem is with the 'southern_european' culture large towns, as this is what the game seems to use for both Gondor and the Dwarves. Definitely no problems with 'nothern_european' settlements (Eriador, etc.) or 'middle_eastern' ones (Rhun, etc.)