"containsKey" and "get" methods are not working properly with "putForExternalRead" during active transaction. WriteSkewException appears.

I'm not new with Infinispan, we use it from 5.3 version. Now I'm working on adding WriteSkew functional to our project, but unfortunately it's not working as we expected.

We use infinispan like a cache for mongoDb data source, but this situation doesn't depends on data source vendor.

The problem is that WriteSkewException is available in specific situation, here are steps for reproducing:
1) begin tx -> create an new element -> commit tx.
2) wait until cache expires. cache is empty now
3) being tx -> try to get element from cache, but it's not found -> load element from data source -> put it to the cache via putForExternalRead for read access outside of current transaction.
4) make some modification with element -> put element to cache -> commit tx -> WriteSkewException

here is my log:
TX BEGIN tx_status=6 thread=1
PUT id=key1, tx_status=0, thread=1 cache_size=1, cache_ contains=key:key1, value:value
TX COMMIT tx_status=0 thread=1
TX BEGIN. tx_status=6, thread=1
SIZE id=key1 tx_status=0, thread=1 cache_size=1 contains=key:key1, value:null
PUT_FOR_EXTERNAL_READ id=key1, tx_status=0 thread=1 cache_size=1 cache_contains=key:key1, value:null
PUT id=key1 tx_status=0 thread=1 cache_size=1 contains=key:key1, value:value
TX COMMIT status=0 thread=1
ISPN000005: Detected write skew on key [1]. Another process has changed the entry since we last read it! Unable to copy entry for update.
Exception executing call org.infinispan.transaction.WriteSkewException: Detected write skew.

I think the problem is in "get" method. When you invoke "get" method with key that not available in cache, infinispan create an "null" element in cache. This element won't be updated by putForExternalRead method (look at log above). If you skip "get" method invocation everithing will work fine. By the way, everithing is working fine if you skip "step 2" of the scenario.

I use workaround for this situation. I check if element exist in the cache not by "containsKey" or "get" method but via cache.keySet().contains(key)
This works ok

I'm looking forward for you comments, maybe I'm doing something wrong.
Thanks