Rule condition is evaluated even if its Ruleflow Group is not active

Issue

Given the rule below:

rule "Some rule"
ruleflow-group "group2"

    when
       p: Person( name.charAt(0) matches "A" )
(...)

It throws an NullPointerException even if its ruleflow-group is not active:

Caused by: java.lang.RuntimeException: Error evaluating constraint 'name.charAt(0) ~= "A"' in [Rule "Second Rule" in rule.drl]
(...)
Caused by: [Error: null pointer: name.charAt(0)]
[Near : {... name.charAt(0) ~= "A" ....}]

Is not the condition side of a rule supposed to be evaluated only when its ruleflow-group is active ?