Kdenlive's config dialog now has the option to use vertical tab bars in its user interface. When checking this option and either pressing OK or Apply, this change immediately becomes effective in the UI. However, when *unchecking* this option and pressing OK or Apply, the change back to horizontal tabs doesn't become effective until restarting Kdenlive. Reproducible: Always Steps to Reproduce: 1. Open Kdenlive's config dialog. 2. In tab "Misc" check "Vertical tab bars in interface". Press Apply. 3. Now uncheck "Vertical tab bars in interface". Press Apply. Actual Results: Tab bars are still vertical -- until next restart of Kdenlive. Expected Results: Tab bars should be horizontal again.
As this bug has been gone, either due to Qt/KF5 upgrades and/or the four-directions positioning of tabs, I'm closing this as RESOLVED/FIXED.