Depends on when you immobilize mabui and on when azure fangs heal her.
If the user casts regenerative healing jutsu together with your combo starting mystery then both your mystery and regenerative healing jutsu are cast BEFORE mabui's standard attack.
In this case you apply the negative status, AF removes it and mabui uses her standard attack and so, before using it, gives 40 chakra.
If, instead, you move first but the AF user isn't quick enough to react (this happens most of the times when the user actually wait to see the icon of the mystery appearing over the enemy ninja) then your action happens before mabui standard attack while his one, if is not fast enough, gets delayed before your 2nd ninja standard attack (if you have higher initiative). In that case mabui wastes her standard attack and so they don't get back the chakra.
What i still have to figure is the interaction with Azure Fang healing justu (the standard attack) because not always the thing work as expected.