At the time of deleting a snapshot from any of the virtual machines automatically deletes from the GUI, but it does not merge into the parent VHD till the VM is off and merge completes. This can cause a major issue if you run out of space and .AVHD keeps increasing. Due to insufficient space to merge the snap-shot, VM will automatically pause.
The only solution to this is monitoring the pending deleted merges by monitoring the following entry in the config file of each Hyper-V VM :
configuration/global_settings/disk_merge_pending = true