macOS 27 developer beta 5 introduces a bug where an NSTrackingSeparatorToolbarItem in a toolbar causes a bar to appear under the toolbar, overlaying the content.
I have a blog post about this at: https://www.virtualsanity.com/202608/nstrackingseparatortoolbaritem-causes-white-bar-over-top-of-content-in-macos-27-developer-beta-5/
I reported this as FB24266969. A sample project and a screenshot are included in both the blog post and the feedback report.
Thank you so much for the post and good description on the issue that I think will be very important to file a bug as may be related to how safeAreaInsets or the NSTitlebarView are being calculated during the initial window layout pass when an NSTrackingSeparatorToolbarItem is present?
I suggestion is to try removing the NSTrackingSeparatorToolbarItem from the default toolbar configuration in the Storyboard and inserting it programmatically in windowDidAppear. Bypassing the initial view load layout pass sometimes prevents these artifacts from rendering.
Do you have a simple focused project you can share in the bug showing the issue?
Once you open the bug report, please post the FB number here for my reference.
If you have any questions about filing a bug report, take a look at Bug Reporting: How and Why?
Albert WWDR
@DTS Engineer Yes, there is a sample project attached to my bug report: FB24266969
You can also download the sample project from:https://www.virtualsanity.com/2026-08-split-view-bug/FullScreenIssue.zip
@johnbrayton Thank you so much for the bug. Got routed to the correct team, give them a few days, but soon they'll reply to you on Feedback Assistant.
For more details on when you'll see updates to your report, please see What to expect after submission.
Albert WWDR
