OS: Windows 10 - 64bit
When selecting multiple files in the Xnview browser the state (enabled/disabled) of the menu items "Open" and "Fullscreen" depends on the order of the multi-selection.
Effect: Irritating user-interface; expected functionality not available
To reproduce:
0. In XnView browser browse a folder with image files (e.g. JPEG files) and non-image files (e.g. DLL files from XnView MP installation).
A1. Select a non-image file
A2. Enhance your selection by pressing Ctrl key and clicking on an image file
A3. Right-click on the image file to open the context menu.
Actual behaviour: menu items "Open" and "Fullscreen" are enabled.
A4. Close the context menu by pressing "Esc" key.
A5. Right-click on the non-image file to open the context menu.
Actual behaviour: menu items "Open" and "Fullscreen" are enabled.
A6. Close the context menu by pressing "Esc" key.
A7. Deselect all files
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B1. Select an image file
B2. A2. Enhance your selection by pressing Ctrl key and clicking on a non-image file
B3. Right-click on the non-image file to open the context menu.
Actual behaviour: menu items "Open" and "Fullscreen" are disabled.
B4. Close the context menu by pressing "Esc" key.
B5. Right-click on the image file to open the context menu.
Actual behaviour: menu items "Open" and "Fullscreen" are disabled.
B6. Close the context menu by pressing "Esc" key.
B7. Deselect all files
Summary of actual behaviour (bug): State of the menu items "Open" and Fullscreen" in context menu depends on the order of your multi-selection. It does not depend on the contents of your multi-selection or on the image that you perform the right-click on.

Expected behaviour: Context menu must not depend on the order of your multi-selection.
Following screen video capture shows the above steps with four files: multiselection_fileliste.wmv.