Preference - Autocompletion - from nth character - can't input value

Description of the Issue

I cannot change the settings for autocompletion after nth character.

Steps to Reproduce the Issue

1. Menu bar, click Settings
2. click Preferences
3. From the box of options on the left, click "Auto-Completion"
4. In the top right of the dialogue box, there is a field to change when Auto-Completion suggestions are triggered. The field shows "From 1 th character".
5. When I click "1" to change it to a different number, a text entry field appears. I am not able to input any number in this field.
6. The setting is stuck at 1th.

Expected Behavior

When I clicked on the field in step 5, I expect to be able to enter any digit between 1 and 9.

Actual Behavior

When I clicked on the field in step 5, I was unable to enter any digit at all.

Debug Information

Notepad++ v7.8.6 (64-bit)
Build time : Apr 21 2020 - 15:23:03
Path : C:\Program Files\Notepad++\notepad++.exe
Admin mode : OFF
Local Conf mode : OFF
OS Name : Windows 10 Pro (64-bit)
OS Version : 1809
OS Build : 17763.475
Plugins : mimeTools.dll NppConverter.dll NppExport.dll

Start by reproducing the issue through Settings > Preferences > Auto-Completion and inspect the implementation of the character-threshold field. Confirm that the field accepts digits from 1 through 9 and that the selected value is retained when the dialog is used.