There is a readOnly optimization that Infinispan does to make sure we don't do a 2PC when there is no data to update. However the code for this does

   public boolean isReadOnly() {
      return (modifications == null || modifications.isEmpty()) && (lookedUpEntries == null || lookedUpEntries.isEmpty());
   }

For repeatable read we always add a value to lookedUpEntries so this optimization never works that isolation level.

Looking closer it seems we do a 1PC when it is readOnly to clean up values, so there shouldn't be a need to care about lookedUpEntries (my guess is this was done as a way to test for locks).