I'm hoping that SourceMod does some twiddling for these values, because the versions in entity_prop_stocks.inc match the single player values in Source SDK 2013's const.h
and not the multiplayer values, which have FL_ANIMDUCKING between FL_DUCKING and FL_WATERJUMP:
#define FL_ANIMDUCKING (1<<2) // Player flag -- Player is in the process of crouching or uncrouching but could be in transition
// examples: Fully ducked: FL_DUCKING & FL_ANIMDUCKING
// Previously fully ducked, unducking in progress: FL_DUCKING & !FL_ANIMDUCKING
// Fully unducked: !FL_DUCKING & !FL_ANIMDUCKING
// Previously fully unducked, ducking in progress: !FL_DUCKING & FL_ANIMDUCKING
Given that this file is essentially from the source code used by HL2:DM, DoD:S, CS:S, and TF2...