There is a mismatch between last version of the isDisjoint relation as specified in the sealed classes spec and its implementation in javac, this should be corrected as otherwise acceptable code could be rejected when class hierarchies are sealed. In particular The main discrepancy I think is caused by the fact that the isDisjoint relation is mostly skipped when at least one of the types being considered is an intersection type.

last spec: http://cr.openjdk.java.net/~gbierman/jep409/jep409-20210507/specs/sealed-classes-jls.html