Hi,
Same as the poster above I am suspecting the context is a 3D NPA where FINAL APP would be the guidance mode used through the APPR p/b.
in some cases where there is no level segment coded prior to the FDP the descent profile is propagated up outwards from the FDP. But there will be a level acceleration segment calculated to reduce from the typical 250: i.e. there is a level segment after the DECEL pseudowaypoint equivalent. Typically this is round about the 15NM mark assuming a decelerated app. When pushing the APPR p/b early you could find yourself inadvertently capturing the level
segment albeit already reduced from 250. The altitude of the level segment is variable and typically between 3000 to 4000 aal. When you satisfy the engagement condition of -150ft you could see FINAL APP engaging and the a/c climbing and possibly even leaving ALT...
sorry for the quick write-up..
brgds