I finally found reproduction steps that work reliably for me every time:
- Enter tab overview mode (View -> Show Tab Overview, or pinch to zoom out on a trackpad from a fully zoomed out state)
- If you have enough tabs open, scroll down so that the window's toolbar/titlebar changes state into the semi-transparent state (tab preview cells are hidden underneath it). If you only have a few tabs open, you'll need to vertically shrink your window to accomplish this.
- Tap on a tab to open it.
- Change the size of your window.
Expected result: Window size changes, titlebar does not go fully transparent.
Actual result: Window size changes, titlebar does go fully transparent.
Note: to resolve this mode, you can either toggle focus mode, or go back into tab overview mode temporarily and select a tab.
Now that I can reproduce it reliably, pardon me while I go fix this adorable but annoying bug 🦖