Have you used r9k ?
Edit: Forgive me for only glancing at the original post at first. I see you have tried it.
BUT: r9kbeta should work… see here:
I’m not sure if TMI ignores r9k, haven’t tested it yet. Also, do you have any other logs that might show if they are putting some extra invisible characters in the string?
R9KBeta
This command disallows users from posting non-unique messages to the channel. It will check for a minimum of 9 characters that are not symbol unicode characters and then purges and repetitive chat lines beyond that. R9K is a unique way of moderating essentially allowing you to stop generic copy-pasted messages intended as spam among over generally annoying content. To find out more about what R9K is, refer to this blog post.
Usage: /r9kbeta
R9KBetaOff
This command will disable R9K mode if it was previously enabled on the channel.
Usage: /r9kbetaoff
Source: Customer Support