The last pool node is failed to upgrade during pool upgrade

Build Info:
indy-node 1.2.45

Steps to Reproduce:
1. Install 1.1.43 pool.
2. Schedule upgrade:

send POOL_UPGRADE name=upgrade_to_the_latest_full version=1.2.45 sha256=ed0a366b4ef36d40c055672a8b83679e99246fec71a706b4ae4cb7958feace3f action=start schedule={'Gw6pDLhcBcoQesN72qfotTgFa7cbuqZpkX3Xo6pLhPhv': '2017-11-17T13:47:00.258870+00:00', '8ECVSk179mjsjKRLWiQtssMLgp6EPhWXtaYyStWPSGAb': '2017-11-17T13:52:00.258870+00:00', 'DKVxG2fXXTU8yT5N7hGEbXB3dfdAnYv1JczDUHpmDxya': '2017-11-17T13:57:00.258870+00:00', '4PS3EDQ3dW1tci1Bp6543CfuuebjFrg36kLAUcskGfaA': '2017-11-17T14:02:00.258870+00:00'} timeout=10 force=False reinstall=False

3. Check the 4th node after its upgrade time.

Actual Results:
The 4th node upgrade doesn't start. Upgrade_log has wrong "cancelled" and "scheduled" entries (they are written with each node upgrade).

Expected Results:
The whole pool should upgrade normally.

Workaround:
Restart the 4th node manually to trigger scheduled upgrade.