SUMMARY
Inadvertently, I inserted the initial characters of the filename in the textbox of the tool "Insert part of filename".
Usually, this textbox shows the filename from which I can select the part to insert.
Now I cannot delete the unwanted characters I inserted, that remains unchanged, instead of showing the original filename.
Reboot has no effect.
The problem remains after reinstall.

STEPS TO REPRODUCE
1. Add some files to rename
2. In Filename tab, click "Insert part of filename"
3. Insert some characters in textbox.
4. Click OK

OBSERVED RESULT
1. In "Insert part of filename" mode, the content of the textbox cannot be edited neither with Canc/Backspace nor edited from keyboard.
2. Selecting part of the textbox, then OK, Kderename uses the selected text to rename the files.
3. Launching Kderename to rename file starting with different characters works OK but trying to rename the initial filename (that starts with the edited characters) has again the same problem.

EXPECTED RESULT
1. The textbox should not be editable, only selectable.
2. After applied the rename, closing Kderename, this textbox should be filled with the first filename to rename.

SOFTWARE/OS VERSIONS
Linux: Ubuntu 18.04.2 LTS
Window Manager: GNOME Shell
GNOME: 3.28.2

ADDITIONAL INFORMATION