Steps to reproduce:

• create/open a project
• click into locator to open the locator window (make sure there's no text currently displayed inside the locator line edit)
• double click on one of the prefixes (a, f, git, ...)
• click into QC's current editor or try to switch applications (Alt+Tab)

Current behavior:

• locator window stays on top

Note: This works fine on OSX (but there it seems as if the locator line edit gets focus again after double clicking the focus, while on Linux it seems as if no widget of QC gets focus) - you can make the window disappear by giving the line edit focus again and clicking somewhere afterwards.