Upgrade 4.2 to 4.3 Blocked

I have noticed that the last few updates to 4.2 have immediately offered a direct upgrade to 4.3 latest if you selected 'Stable 4.3' in the update channel after upgrade. If you wait sometime though, this stops being offered. As per https://access.redhat.com/solutions/4780021 this is a known bug with no ETA to be fixed. That's fine but why is the platform offering the upgrade for a short period? If you do the upgrade quickly it does work!