Reproduction steps:

1. Start Qt Creator, select Tools->Options->Locator.
2. Change the Methods prefix from "m" to another character, such "n"
or "x" by clicking "Edit" button. Click "Apply" button, then "OK"
button.
3. Input "n" or "x" in the locator, you can also use ctrl+k. By this the
locator page is blank, see locator.png.
4. Select Tools->Options->Locator again.
5. Change the Methods prefix from "n" back to "m". Click "Apply" button,
then "OK" button.
6. Select Tools->Options->Locator for the third time. And the page is
blank see locator3.png.
7. Use the locator. It is blank when nothing input into it.See
locator2.png.