Bug in the message scheduling

Steps to reproduce:

1. A message is scheduled on the empty Azure ServiceBus Queue
2. The message scheduling is cancelled using its <g class="gr_ gr_158 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling ins-del multiReplace" data-gr-id="158" id="158">scheduleId</g> after becoming active but before it is processed by the receiver
3. The message is still active and the number of scheduled messages (visible on the Azure portal) is decreased by 1 (even below 0)

... so if there was just 1 message scheduled that is now active and being <g class="gr_ gr_791 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling multiReplace" data-gr-id="791" id="791">cancelled</g> then the number of messages in the schedule queue stands at -1. 

This is appearing in ServiceBus service as of 26 of July 2018