'format not determined' warning does not appear

[marsh]

When opening an unsupported file, the warning message "Format of the file <abcd.efg> could not be determined" usually appears.
The new problem:
The warning is not shown when there are multiple files in a directory.
The warning is shown, as expected, when only 1 file is in a directory.

[xnview]

When opening an unsupported file, the warning message "Format of the file <abcd.efg> could not be determined" usually appears.
The new problem:
The warning is not shown when there are multiple files in a directory.
The warning is shown, as expected, when only 1 file is in a directory.

How do you try to open it?

[marsh]

When opening an unsupported file, the warning message "Format of the file <abcd.efg> could not be determined" usually appears.
The new problem:
The warning is not shown when there are multiple files in a directory.
The warning is shown, as expected, when only 1 file is in a directory.

How do you try to open it?

Using browser + <enter>
Other settings:
Switching modes: browser>fullscreen>viewer.
Open action: All other files: Open in Xnview.
Browser's small toolbar filter set to all (for displaying non-image files).

[helmut]

I could reproduce your problem with default settings:

1.) Browse a folder with one single non-image file.
2.) In context menu (right mouse click) choose "Open".
--> A message box "Format of the file <xx> could not be determined" appears


3.) Make a copy of the non-image file in the same folder (there are two non-image files in the folder, now).
4.) In context menu choose "Open".
--> No message box appears.

Note: Amazing that you (marsh) have found out that it makes a difference whether there is one single file or whether there are multiple files!