With the latest snapshot. running the attached code twice generates the error below.
The intent to create or update a database from the data files.

Regards

Improper use? Potential bug? Your feedback is welcome:
Contact: basex-talk@mailman.uni-konstanz.de
Version: BaseX 8.0 beta 07cd3e9
Java: Oracle Corporation, 1.7.0_60
OS: Windows 8.1, amd64
Stack Trace:
java.lang.RuntimeException: Insertion at beginning of populated table.
    at org.basex.util.Util.notExpected(Util.java:60)
    at org.basex.io.random.TableDiskAccess.insert(TableDiskAccess.java:325)
    at org.basex.data.Data.insert(Data.java:915)
    at org.basex.data.Data.insert(Data.java:806)
    at org.basex.data.atomic.Replace.apply(Replace.java:64)
    at org.basex.data.atomic.AtomicUpdateCache.applyUpdates(AtomicUpdateCache.java:298)
    at org.basex.data.atomic.AtomicUpdateCache.execute(AtomicUpdateCache.java:282)
    at org.basex.query.up.DataUpdates.apply(DataUpdates.java:164)
    at org.basex.query.up.ContextModifier.apply(ContextModifier.java:110)
    at org.basex.query.up.Updates.apply(Updates.java:133)
    at org.basex.query.QueryContext.iter(QueryContext.java:348)
    at org.basex.query.QueryContext.execute(QueryContext.java:590)
    at org.basex.query.QueryProcessor.execute(QueryProcessor.java:100)
    at org.basex.core.cmd.AQuery.query(AQuery.java:82)
    at org.basex.core.cmd.XQuery.run(XQuery.java:22)
    at org.basex.core.Command.run(Command.java:360)
    at org.basex.core.Command.execute(Command.java:94)
    at org.basex.gui.GUI.exec(GUI.java:470)
    at org.basex.gui.GUI.access$5(GUI.java:427)
    at org.basex.gui.GUI$8.run(GUI.java:414)