Macros go good with a side of French Onion dip, for sure!
All jokes aside, Macros are scripts that can be performed after a keystroke or button press. It allows Moderators to store useful phrases and links to respond efficiently in situations that occur regularly and warrant the same response or action (such as posting the Report Abuse link or Ban Dispute link in the Hub).
In response to the question, this is an interesting bug. I'd recommend letting Devin know on the bug report email (
[email protected]). I'm sure the developers already know about this, considering it's a fairly signifcant bug that's sure to affect quite a number of users staying on 1.6.4 to use OptiFine, but it never hurts to double-check and make sure!