There is contents tree on left side of application window of Khelpcenter.
If you select "Single click to open files and directories" in application "System Settings" in menu "Input devices" -> "Mouse", upon single click on any expandable item in contents (let's for example take "Application Manuals" or "System Settings Modules") it expands, upon double click it swiftly expands and collapses back. If it's already expanded, it collapses, and on double click it collapses and expands back.
However, if you select "Double click to open files and directories (select icons on first click)" in "System Settings", you no longer can expand/collapse any expandable items in Khelpcenter's contents tree using mouse clicks. You need to double click to expand it, and in best case you can see it swiftly expanding and collapsing back if it's collapsed, or vice versa if it's expanded.
It looks like with "Double click" setting selected contents item receives two events on double click: "selected" and "double click". On first event "expanded/collapsed" state is toggled via explicit calls to corresponding functions (see function Navigator::slotItemSelected), on second event this state is toggled again, thus reverting it to original state. This patch sets a specific setting to get rid of second event and make behaviour similar no matter which mouse settings is used, "single click" or "double click".
BUG: 399275