Oracle "opidcl aborting process unknown ospid (xxx) as a result of ORA-28" error.

If you get following ORA errors in your database alert log:
"opidcl aborting process unknown ospid (xxxx) as a result of ORA-28"

This usually means that some privileged user (dba) has killed sessions from database.

But if you see these errors a lot or all the time then this can be bug. This bug is affected
older (Oracle 11.1.0.6 and 11.1.0.7) versions. With bug error messages look like this:
"ORA-28 : opiodr aborting process unknown ospid (xxxxx_xxxxxxxxxxx) "

NOTE! If some application or user kill several (for example all one user) sessions at the same time there can be several errors in a row in alert log and it is still a normal situation.