I discovered a bug in my application that only occurs in OSx Mavericks (10.9) but works on all others (10.7 - 10.8).
It will take some time to fix it, but I still want to release for the others.
Do you know if it is possible to exclude Mavericks from the mac app store. I have seen people filtering based on mac model for performance reasons. What would be the best approach other than fixing the bug obviously?
You cannot exclude a later OS version in the Mac App Store. If you have a workaround (disable feature or something) on Mavericks then you can check the OS version on runtime (see OS X version checking in Cocoa) and submit a new version to the Mac App Store and request a expedite review.