Description of problem:
register host to satellite-6.2.5, set cpu.cpu_socket(s) to 8 on host, then attach 8 quantity "Instance Based" subscriptions (SKU: RH00003) to host by several times via subscription-manager-gui, will auto attach an extra subscription after the second time attach.  
 

Version-Release number of selected component (if applicable):
subscription-manager-1.18.5-1.el6.x86_64
python-rhsm-1.18.5-1.el6.x86_64


How reproducible:
always


Steps to Reproduce:
1.register host to satellite-6.2.5
# subscription-manager register
Registering to: bootp-73-3-223.eng.pek2.redhat.com:443/rhsm
Username: admin
Password: 
Organization: Default_Organization
The system has been registered with ID: 1a0032d8-26a0-40ff-a346-1a271c14d4da

2.set cpu.cpu_socket(s) to 8 on host
# echo '{"cpu.cpu_socket(s)":"8"}' > /etc/rhsm/facts/custom.facts
# subscription-manager facts --update
Successfully updated the system facts.
# subscription-manager facts --list |grep cpu.cpu_socket
cpu.cpu_socket(s): 8

3. attach "Instance Based" subscription to host by GUI
#subscrition-manager-gui
  1). go to "All Available Subscription" tab, click "update" button
  2). choose the Instance Base subscription, modify the quantity spinner to 2, click "attach" button, check "My Subscriptions" tab, will success to subscribe 2 quantity; but check "All Available Subscriptions" tab, the "Available" and "Quantity" reduce 8, not 2.
  3). modify the Instance Base subscription quantity spinner to 2 again and click "attach", check "My Subscriptions" tab, list 3 Instance Base subscriptions with quantity 2, 2 and 6, the extra subscription with quantity 6 is auto attached; check "All Available Subscriptions" tab, "Available" reduces total 10.


Actual results:
Auto attach an extra "Instance Based" subscription

Expected results:
Subscribe as the quantity spinner setting.