Hello Marco,
I belive mentioned problem is not related to DB at all and should exist on many DBs. We saw this on DB2 UDB 9. Problem roots reside in JPBM5 persistence mechanism design, it should be reviewed and reworked, palliative solution to bypass this provided above. ORM works with entities like processinstanceinfo (XXXinfo), but there is no correlation between real process runtime info and serialized XXXinfo. Once XXXinfo is serialized by ORM, it will not be serialized anymore even if related process was updated. In 90-99% cases nobody see this problem, as in JBPM5 demo, presentation and tutorial code transaction is simple and commit happens at the end, when all JBPM5 execution finished and all is good. In real business application and large transaction it's possible that Hibernate sometime flushes data to DB in the middle of JTA transaction. This intermediate snapshot will contain old/broken information about process instance. Later, at the JTA transaction commit time latest process instance information will not be serialized to DB anymore.
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Thanks,
Vadim.