Weird copter behavior battery failsafe triggered rtl while flying althold?

hi all,

succesful autotune and disarm. while hdop is 0.65 fly start in loiter. while flying in althold mode battery failsafe rtl angaged but copter did not stoped and rise to come home. i tried to rise copter with throttle but not succes. copter moved like freewheeled car in rtl mode. copter may flew about maybe 15 meters long and crush into tree. is it normal to move that long distance when batteryfailsafe angaged rtl in althold mode?. i want to know if this result will be the same if i were in loiter mode or not?

frame:TBS discovery
motors:sunnysky 2212 980kv
prop: gemfan 8045 nylon carbon gemfan (balanced)
gnss module: Ublox m8n
esc:favorite little bee blheli 30a (oneshot125)
receiver: flysky fs-ia6b
transmitter: flysky fs-ia (ibus)
lipo: 4s 2200mah 70c cnhl
arducopter : ArduCopter V4.0.3 (ffd08628)

here is the link of log and params file

thanks in advance
┼čakir polay