SUMMARY
When starting Dolphin with Split view enabled and without remembering the last used folders and tabs, the two split view panes end up in a weird limbo state of splitting the keyboard and mouse focus between them, while both are looking as if they were "sort of focused" (see screenshot).

STEPS TO REPRODUCE
1. Start Dolphin, go to Settings -> Interface -> Folders & Tabs
2. Select "Show on startup: /home/yourusername (or any other folder)"
3. Enable "New windows: Begin in split view mode"
4. Close Dolphin, start Dolphin again.

OBSERVED RESULT
* Both split view panes have the same background color, and the location bar is grayed out on both panes.
* The left pane has keyboard focus (to test, press arrow down on keyboard), but the right pane has focus for opening folders via mouse click on the places panel, and also for the toolbar button that closes the active split view pane!
* This weird state is ended by either opening a directory via double-click in one of the split views, or by opening one of Dolphin's modal dialog windows (like Settings, Keyboard Shortcut configuration etc.).

EXPECTED RESULT
Visual distinction which of the two panes has focus, with both keyboard and mouse focus applying to the same pane.

SOFTWARE/OS VERSIONS
KDE Plasma Version: 6.3.80
KDE Frameworks Version: 6.14.0
Qt Version: 6.8.3

ADDITIONAL INFORMATION
Reproduced with
* Dolphin + Plasma build from master on Kubuntu 25.04
* Neon Unstable live image in a VM

On Dolphin 25.04 (Neon User live image) the bug is absent, so it seems to be a recent regression on master.