The stall AOA is set to 15° in the lift_coef_aoa_table, the stall protection system is disabled, the simulated stall speed is around 140 kts and the estimated stall speed is 157 kts. The aircraft is not fly-by-wire.
However, as soon as incidence is reaching 11.8°, a nose down command is given (clearly visible on the FD) and the aircraft enters a gentle descent, but doesn't stall and doesn't even get close to the stall AOA of 15°.
Test conditions are ISA, 15.000ft, AP engaged in ALT HLD and HDG HLD, A/T off and thrust to idle.
There is plenty of pitch authority left as the trim is not reaching 100% deflection.
Any idea of what could be causing such a behaviour?