According to the log the rule is evoked, but the subject of the mail is completely empty. The original subject and the tag are missing.
16:01:21.469 2 QUEUE([5648818]) from <info@ems.ch>, 868 bytes (<FileMaker.53f0b5b1.b.14501@>)
16:01:21.532 4 LOCALRULES(info) rule(Filemaker) conditions met
16:01:21.532 2 LOCALRULES(info) [5648818] rule(Filemaker): subject tagged: '[FM-INFO]'
The weird thing: the same rule, when evoked by mails with a different return path is working correctly!: the tag is added before the original subject, as expected.