Hi,
Check nature and properties of tax condition type JMOP ( and JMX1) details in t.code;OBYZ. such as exclusion indicator if any!
Also check are there any routine presence for condition type JMOP (and JMX1) in your tax procedure in t.code;OBYZ. Cross check 16 columns for condition type JMOP (and JMX1) in your tax procedure
Have look on setting condition type JMOP (and JMX1)
http://wiki.sdn.sap.com/wiki/display/ERPLO/Difference+between+TAXINJ+and+TAXINN
Thanks & Regards,
Biju K