The problem is that there is only one autoinc value associated with 
the query when binlogging. If more than one autoinc values are used 
in the query, the autoinc values after the first one can be inserted 
wrongly on slave. So these autoinc values can become inconsistent on 
master and slave.

The problem is resolved by marking all the statements that invoke 
a trigger or call a function that updated autoinc fields as unsafe, 
and will switch to row-format in Mixed mode. Actually, the statement 
is safe if just one autoinc value is used in sub-statement, but it's 
impossible to check how many autoinc values are used in sub-statement.)