Start the editor with e.g. any cpp file, take any word you like that is in the text or not, press Ctrl+F.
The Search line opens within the editor window, start typing e.g. "foo". Now if you decide to search for something completely else like "bar", normally (in nearly every other software) you press Ctrl+F again, and then the whole search line gets highlighted, so you can just start typing your new search term.

Not in QtCreator, there just the search QLineEdit receives the focus, and the cursor is at the end, so if you write "bar" the line will read "foobar" instead of "bar".

This is unconvenient and unusual.