Wow, weird problem man
I don't own the gun personally but if everything is working when it's detached, I'd guess that the trigger guard or hole in the stock for the trigger to poke through is chafing it. Or perhaps one of your stock screws is hampering the trigger function (for instance, I know the trigger guard on the vsr-10's attaches to the trigger unit itself).
It might be a problem with sears misaligning themselves, if you can (sometimes it's impossible to cock this way) shoot the gun for a while without the stock, see if the same problem happens.
Sorry I can't be more help, I've got very few ideas on this.
I don't own the gun personally but if everything is working when it's detached, I'd guess that the trigger guard or hole in the stock for the trigger to poke through is chafing it. Or perhaps one of your stock screws is hampering the trigger function (for instance, I know the trigger guard on the vsr-10's attaches to the trigger unit itself).
It might be a problem with sears misaligning themselves, if you can (sometimes it's impossible to cock this way) shoot the gun for a while without the stock, see if the same problem happens.
Sorry I can't be more help, I've got very few ideas on this.