Thumbnails - some are smaller than they should be

[Fledi]

Some thumbnails don't use the whole space even if the file has the same dimensions, dpi, format as an other file.
I have saved the file again and reloaded but the thumbnail is smaller than the others.

I have set the thumbnails to 300x300px and most of the thumbnails are correct but some have only half size.

[Bhikkhu Pesala]

Please attach the original images.

[Fledi]

If I edit a file in Photoshop CS6 than the thumbnail will be shown in a smaller version.
If I deselect "try to load EXIF-Thumbnail for JPG Files" than the size is as it schould be.
So for me that is a workaround but it should definitely be fixed.

I checked the differences between a photo before editing in photoshop with the result afterwards and one of the differences ist that:

?

There is a fixed resolution for the thumbnails which is set by phtotoshop

So in order to work properly irfanview has to overwirte this part of the exif Information.

[Bhikkhu Pesala]

It is hard to see how this is a bug. Maybe the option was not available in earlier versions?
I checked, and the option was available in 4.60.