I've added a test case for this.
it can be found at https://github.com/calbazasebastian/jbpm/commit/7090a13a983d35035fe43e6a23040b23a200b346
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1. create process definition that consists of start -> user task -> timer -> end
2. start process (this returns control as soon as task is completed)
3. complete human task (this returns control as soon as timer is scheduled in memory)
4. dispose session
5. load session from db
process is waiting on timer node without timer being triggered