Rules are not fired when String attribute is evaluated with 'attrib=="value"'

Issue

We have rules like the following, where a String attribute of an Object is evaluated in the LHS of the rule:

  rule "rule12"
  when 
     Line(type=="12")
  then
  end

However, we noticed that we also have rules where the check is done without any quotes, mixed with other rules where quotes are used:

  rule "rule11"
  when 
     Line(type==11)
  then
  end

  rule "rule11a"
  when 
     Line(type=="11")
  then
  end

As a result some rules are not fired. If we insert a Line object with type="11", we expect the two rules to be fired. However, only one rule is fired.