Slitherine

I've been through the Kursk scenario a couple of times now. Near the end, when there are only a couple of objectives left, I noticed the AI purchases a large number of T70 units. These then move but do not attack. I am wondering if this is by intent, and if so, why do they not attack in an attempt to disrupt the Axis rear or flanks of a thrust or is it a bug.

Apologies in advance if this has been brought up before.

On what difficulty level are you playing?

AI did this to me on Manstein setting, but it's a fairly rare occurrence.

It seems to happen when:
AI is low on victory hexes.
AI has maxed out purchases on remaining VHes (no room).
AI still has prestige to spent.

Then you get a mass of cheap tanks purchased near by.

It was on General difficulty.