I found that even when using no AO switching form standing to crouch animation state takes two pagedown key press instead of one when we follow this animation state sequence: crouching > ground sit > standing > crouching.

When the animation state sequence is this: standing > ground sit > standing > crouching, then only one pagedown key press triggers crouching.

This happens only in Firestorm viewer when "Enable Crouch Toggle Mode" is enabled.