"In selection" checkbox greyed out although there is a selection

Description of the Issue

Sometimes, although there is a selection, the "In selection" checkbox is greyed out in the Find / Replace / Mark tabs of the Find / Replace / Find in Files / Mark dialog box. I should not be greyed out when there is a selection. This does not happen always. See steps to reproduce the issue the simplest way.

Steps to Reproduce the Issue

1. Open Notepad++ 7.9.3 on Windows 10
2. Type "Hello" (no quotes)
3. Select Search then Find in the menu : "Hello" appears in "Find what", and the "In selection" checkbox is greyed out
4. Press ESC to close the dialog box
5. Select Search then Find in the menu : "Hello" appears in "Find what", and the "In selection" checkbox is greyed out
6. Press ESC to close the dialog box
7. Select Search then Find in the menu : "Hello" appears in "Find what", and the "In selection" checkbox is NOT greyed out

Expected Behavior

The "In selection" checkbox should not be greyed out when there is a selection, be it a manual or an automatic selection.

Actual Behavior

The "In selection" was greyed out although "Hello" was selected when the Find dialog was opened the second time.

Debug Information

Notepad++ v7.9.3 (64-bit)
Build time : Feb 14 2021 - 03:15:58
Path : C:\Program Files\Notepad++\notepad++.exe
Admin mode : OFF
Local Conf mode : OFF
OS Name : Windows 10 Pro (64-bit)
OS Version : 1909
OS Build : 18363.1379
Current ANSI codepage : 1252
Plugins : mimeTools.dll NppConverter.dll NppExport.dll

Start by reproducing the sequence in the Find / Replace / Find in Files / Mark dialog, using the selection and repeated open-and-close steps from the issue. Trace how the dialog decides whether the "In selection" checkbox is enabled. Done means the checkbox is enabled whenever a manual or automatic selection exists, including after reopening the dialog.