You cannot go up steep stairs while facing forward with your weapon raised. Buildings affected are the Military Cargo Post (<i>Land_Cargo_Patrol_V1_F</i>), Military Cargo HQ (<i>Land_Cargo_HQ_V1_F</i>) and possibly others.

I suspect it is caused by the collision geometry for the given animations being changed as per:

<i>Assigned new style collision envelopes to movement with rifle. This should fix several issues with clipping, sticking and walking through walls. Also improves character handling, as the rotation axis is now moved under characters head, instead of it's feet. Pistol envelopes remain old-style for comparison, but will shortly follow.</i>

The problem affects:

• Up rifle raised walk
• Up rifle raised tactical
• Up rifle raised run
• Up rifle raised evasive
• Middle rifle raised walk
• Middle rifle raised tactical
• Middle rifle raised run
• Middle rifle raised evasive
• Up pistol raised run
• Up pistol raised evasive
• Middle pistol raised walk
• Middle pistol raised tactical
• Middle pistol raised run
• Middle pistol raised evasive

You can convince it to let you go by turning to the side.