Invalid code generated after instanceof test

01| class Base { String getName() { ... } }
02| class SubclassA extends Base {}
03| class SubclassB extends Base {}
04| 
05| def instance = produceSubclassInstance()
06| instance?.with {
07|     if ((some other condition) || (instance instanceof SubclassA)) {
08|         someMethod(instance.name)
09|     }
10| }

org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'SubclassB@...[...]' with class 'SubclassB' to class 'SubclassA' 

06| if (instance != null) {
07|     if ((some other condition) || (instance instanceof SubclassA)) {
08|         someMethod(instance.name)
09|     }
10| }