The selection sequence from top down is
- number of monitored interfaces which are 'up' (greater number wins)
- age = uptime (greater number wins)
- priority (greater number wins)
- serial number (greater number wins)
So, in your example, you force a switch to the other unit by pulling a monitored port's cable on the current master. This will decide it on the first check, regardless of age, priority or serial number.
But, as I've pointed out, setting the override option will change that sequence: priority will then come first, before age. So if override is enabled, and priority of the unit joining the cluster is higher, the joining's unit configuration will overwrite the current master's. That's the situation to be aware of.
@jmlux: are you reading this at all?
"Kernel panic: Aiee, killing interrupt handler!"