Our application is trying to read all resolutions of an external monitor. We have observed that, for the external monitor there is a mismatch in resolution list in our application and the resolution list in system settings. We are using the apple API "CGDisplayCopyAllDisplayModes" to read the resolutions.
Our engineering teams need to investigate this issue, as resolution may involve changes to Apple's software. Please file a bug report, include a small Xcode project and some directions that can be used to reproduce the problem and detailed information about your monitor. Please post the FB number here after filing a bug report. If you post the bug number here I'll check the status next time I do a sweep of forums posts where I've suggested bug reports.
Bug Reporting: How and Why? has tips on creating your bug report.