Dear Armand,
I think that you somewhat misunderstand the composition of the opolchenie (militia). They were typically not serf. They were volunteers.
In areas near Petersburg and Moscow, they would be mostly free traders and craftsmen, with some factory workers (some of these might be government serfs, but still they were more or less skilled paid workers). In the south and east, the militia would be again free, the people of Cossack or similar social position. In the north, again free – forresters, hunters, trappers, lumbermen, Protestant Finns and Baltic "Germans", and so on. Some nobles, due to poverty or zeal or both, also volunteered for the ranks.
These kind of folks had a lot on the line in serving in the militia
. not just the usual risks, but also the chance for their family to get officially recognized for their service – and perhaps advance to the Russian or Cossack (and similar) nobility. I do not know of any case where they ran away under combat. It may have happened, but I never heard of it. It would have ruined a family's reputation.
I know of one instance where their was tumult or semi-mutiny. It was during the forming-up of the Kostromo opolchenie. A rumor went around that they were being taken into the Army. This would have been (i) for 25 years, instead of the duration of the war, and (ii) a reduction to a nearly serf-equivalent soical status. But when the situation was clarified, the tumult stopped and everyone started apologizing to each other.
There were some serfs in the opolchenie. For example, volunteers from the empannage properties (personal holdings) of the Imperial family. Great units of light infantry, including the L.-G. Finns, were formed from these volunteers. Also, a noble might bring a few serfs with him (for servants, for bodyguards, to make the local recruitment numbers look good). But, oddly, the whole "tone" or culture of the opolchenie was rather bourgeois and Cossack, instead of serf.
I could also add that the opolchenie were "leavened" with detachments from their training battalions (mostly Marines for the Peterburg militia), the healthiest/youngest memebers of the local Internal Guard (like gendarmes, more or less) and retired soldiers from military settlements.
On another topic
.
I think 300 rioters was not so many, in your example. I think Dr. Lieven is merely taking advange of the Graf Vitgenshtein's headquarter's' generally competent staff work, active reporting, and the accident of almost a complete set of surving documents. I am sure 300 person riots were not uncommon at all in places were the French were moving through. Didn't the French shoot 3000 or so in Moscow? I know of no examples of serf uprisings away from the French army. But, I have never looked carefuly for such.
That said, you may recall that this region near Vitebsk had been part of the Polich-Lithuanian Commonwealth into the 1770's or 1790's.
See map
The people here may be ethnically Belarussian or Polish-Lithuanian. Many were Catholic. So, having little taste for obedience to Russian masters that look like they may be losing a war
. well, not too surprising. More surprising is the generally marked loyalty of the recently occupied Finnish and Baltic peoples.