Spies and unrest

[thejeff]

Unrest does not affect gems.

I've noticed something odd about catching spies.
SP game, playing MA Ulm, I've had a bunch of spies causing unrest in Pythium's capital for awhile now. He rarely catches any, but when he does he seems to catch all of them.
The first time, I'd just started and assumed he'd just boosted his patrollers. The second time I already had roughly 150 unrest there. He had the standard capital 25 PD and judging from the troops that attacked my poor spies another 60 or so patrolling. With the penalty from unrest his chances should have been slim, but he caught all 4 spies.

Is the roll only made once for patrolling, so if he got a good open-ended roll all stealthy units are likely to be caught?