ClassCastException when using expireStoreSize on heap store

[BF]

Hello,

I have the following setup in a unit test:

final Serializer valueSerializer = new ValueSerializer(); //CUSTOM serializer
HTreeMap<String, Properties> diskStore = DBMaker.tempFileDB().make().hashMap("disk", Serializer.STRING, valueSerializer).createOrOpen();
HTreeMap<String, Properties> heapStore = DBMaker.heapDB().make().hashMap("heap", Serializer.STRING, valueSerializer)
                    .expireOverflow(diskStore)
                    .expireStoreSize(100)
                    .expireAfterCreate()
                    .createOrOpen();

// populate store
for (int i=0; i<100; i++) {
    Properties prop = new Properties();
    prop.setProperty("index", i + "");
    heapStore.put("props" + i , prop);
}

diskStore.close();
heapStore.close();

What I want here is to be able to store only 100B on heap and the rest of the records to overflow to disk. However, while running this code I get the following exception:

java.lang.ClassCastException: org.mapdb.StoreOnHeap cannot be cast to org.mapdb.StoreDirect

    at org.mapdb.HTreeMap$expireEvictSegment$1.take(HTreeMap.kt:875)
    at org.mapdb.QueueLong.takeUntil(QueueLong.kt:153)
    at org.mapdb.HTreeMap.expireEvictSegment(HTreeMap.kt:859)
    at org.mapdb.HTreeMap.put(HTreeMap.kt:322)

Could you please take a look?

Thanks!