I'm not sure if I understand your issue exactly, but one possible cause could be that the "_" is a wildcard for the LIKE expressions. If you try to find text using
WHERE somecolumn LIKE '__a'
the underscores indicate any single character. So this would match 'aaa', '__a', 'bba', etc. If you want to match "_" you will need to escape it. One way to do this is:
WHERE somecolumn LIKE '[_][_]a'
Regards,
Andras
Andras Belokosztolszki, MCPD, PhD
GoldenGate Software