pineteam
In managed descent aircraft goes through repressurisation(when applicable), idle thrust and geometric segments and it will try to maintain its vertical profile. ATHR will keep changing from idle to speed mode as required to keep speed. If you were in OP DES where there is no vertical profile and added/reduced thrust the aircraft will pitch up and down to maintain speed. But in managed descent if you were on profile and added thrust the FMGC will force it down to stay on the profile so speed will increase. Nothing surprising.