Evaluation of facts hasn't been affected by 'modify()' when parsing String to Double

rule "Rule 1" salience 30 when then Resource resource1 = new Resource(); resource1.setName( "Resource 1" ); resource1.setAmount( "5" ); insert(resource1); System .out.println( "First" ); end rule "Rule 2" salience 20 //no-loop - next rule fires if use 'update()' instead when $resource1: Resource(name == "Resource 1" ) then modify($resource1) {setAmount( "20" )}; // update($resource1); System .out.println( "Second" ); end rule "Rule 3" salience 30 when $resource1: Resource(name == "Resource 1" , Double .parseDouble(amount) == 20.0) // - interesting that the line below fires this rule // $resource1: Resource(name == "Resource 1" , amount.startsWith( "20" )) then System .out.println( "Rule is fired" ); //doesn't fire end

So why it works with java String methods, but doesn't with Double parsing? And I try to walk away situations of using 'update()' as it is being noted often in books about Drools. Because when I have a lot of rules updating may brake my saliences leading to unexpected executions.