Okay - This must be pretty obvious if you don't come from SAP SQL but apparently updates also hold a cursor open for results and it's actually simply to do with closing the result set in your call to execute query (based on my indicative testing and the note info). e.g. Try this in your code and see if you can get any further (fingers crossed):
data(lo_result) = lr_sql->execute_query( LV_QURREY ). lo_result->close( ).
Cheers,
Matt