Tron

Enemies climbing onto roofs is really normal. Here's the fastest way to reproduce it: Start a new game, hire a merc, right after the heli drop climb onto the roof of the house right next to the drop zone, lay down and hide up there. Wait for the enemies to reach the drop zone. Now make yourself seen shortly (e.g. fire at one enemy on the ground) and duck again. Now just wait for them to climb onto the roof.
As far as I understand, enemies climbing onto roofs was broken by some change in JA2-1.13 and only repaired recently. I am not aware of such a problem in JA2-Stracciatella.

I tried 12 times with different mercs from AIM and it was 100% failure.

Then I tried with a binary built with the BETAVERSION and TESTVERSION compile-time options on and it was a success for all my 4 tries.
All the enemies climbed each time.

Then I tried again the no BETAVERSION and no TESTVERSION program and it was 100% failure (2 tries).

Then with the BETAVERSION and TESTVERSION program and it was 100% success (2 tries).

And finally:
The BETAVERSION only option gave me one failure for one try
The TESTVERSION only option gave me one success for one try