OS: Windows 10 - 64bit
In all(?) multiline textfields the user cannot navigate to the next field by pressing "Tab" key. Neither Tab key works, nor Strg+Tab.
Effect: User cannot fill out dialogs using keyboard, only.
To reproduce:
1. In XnView browser select one or multiple images.
2. Select Create » Contact sheet...
3. In "Create contact sheet" dialog press Tab key till focus is in field "Information".
4. Press Tab key one more time
Actual behaviour (bug): A tab character is inserted into the Information field.

Expected behaviour: Tab key should tab to the next field. Strg+Tab should insert a tab character into the Information field. (On Windows Strg+Tab is de-facto standard keyboard assignment for inserting tab character).
Note: The above example is for the dialog "Create contact sheet" but it applies for other dialogs like "Edit IPTC", too.