Some additional information:

• When using EHCache as the jsr107 impl, there's no exception thrown, but the query results are not cached (see my PR comment for details) => that's probably why the bug went unnoticed so far
• With other JSR107 impls, like the RI or Caffeine, the problem is obvious (and blocking) because a serialization exception is thrown

Any chance this could be fixed in 6.2 ?