Performance issue with a Fighters Guild quest

Running OpenMW 0.40 on an Atom z3735f/2gb/Ubuntu 16.04 system.

Hi, I am encountering a big performance issue on a Fighter Guild mission, the Telvanni Agents.

When I am approaching to the mine near to Caldera (Ashanammu), outside I see the guard with the bow. I chat with him and he wants to fight against me, it happens as:

• He shoots me an arrow bow (?);
• I attack him;
• He is retiring, flying backwards

and in this exact moment, the scene rendering becomes REALLY slow (from about 30 fps to 4-5), with an huge performance regression.

This is strange, since I haven't seen this regression during all the game.

(RM-3631 from redmine: created on 2016-11-21 by Luca Chess, , closed on 2017-01-01 by nobody, duplicates #3355 (closed))