When running Schema Compare, it finds differences for triggers that show no script difference when I use the "File Difference" viewer. I don't see any script differences in the schema browser either. It notes "Differs by description" under Compare's "Results (interactive)".
There is a difference in the triggers's description. To verify this, run the following query on the schemas you are comparing. You can specify with
SELECT description FROM USER_triggers WHERE trigger_name = <name of your trigger>;
Verify Option setting in Schema Compare tool. Under Options tab, there are difference options you can set to adjust the comparison of your schemas (Misc Options and Object Type Specific Options).
For triggers with "Differ by description" try adjusting:
Options | Object Type Specific Options | Triggers section | enable "Don't comp schema name in description".