Is misting a casing going to cause pins to abort ?
No, gently misting the casing won't make pins abort.
The rule is to never water the casing heavy so that it is really wet but mist it gently from time to time so the casing remains moist all the time. The keyword is moist. Heavy watering could harm the pins and it will also seal the casing surface and make the conditions less favorable for the mushroom formation. But misting is OK and necessary.
Try not to mist the bigger mushrooms directly since this can cause mushroom rot. At this stage try to mist the casing surface between them, although a few drops directly on the mushrooms won't do any harm.
