Format rules based on child records not working correctly?

I have a formatting rule with this conditional expression:

count( select([manholes][key] , [hose pull] > 30) ) > 0

When testing from the expression assistant, it returns true for the appropriate records, but it does not change any formatting. However, I made a copy of the rule, and changed the condition expression to:

[hose pull] = true

and added a new [hose pull] VC with a similar expression:

IFS( count( select( [manholes][key] , [hose pull] > 30 ) ) > 0 , true)

And that rule successfully changes the formatting. What’s going on here?

I’m able to successfully use singular derefs in format rules, so perhaps this is specific to bulk derefs?