Harsan airmax

Ok , I know someone in here can answer my questions.
I have a Hatsan Airmax .
I bought tha male adapter for the Hatsan filling probe , after charging when I go to remove my probe , it pops or snaps . I've refilled it 3 times , an 3 times it has done the same thing .
I'd appreciate if someone could tell me why ??
Thanks
 
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