GraphDB Rulesets are not correctly removed (GraphDB 9.10 SE)

Question

Recently, I have been working on managing rulesets in a GraphDB repository using SPARQL.

First I create a ruleset using:

INSERT DATA {
    <_:custom> sys:addRuleset
        '''Prefices { a : http://a/ }
           Axioms {}
           Rules
           {
           Id: custom
              a b c
              a <a:custom1> c
              -----------------------
              b <a:custom1> a
           }'''
}

Then I list the rulesets by using:

SELECT ?state ?ruleset {
    ?state sys:listRulesets ?ruleset
}

and see that custom has been added.

At this point, I decide to remove custom with:

INSERT DATA {
    _:b sys:removeRuleset "custom"
}

and yet, when I list the rulesets again, "custom" still appears.

Is this a bug?

I am using GraphDB SE 9.10.