First off, my setup:
I have three monitors in landscape orientation which through nVidia Surround are seen as a single ultra-wide monitor. I use DisplayFusion's Monitor Configuration to split this back into three virtual monitors, and then let DF apply a single wallpaper image to all screens so I have a nice stretched setup tailored for me.

DF also has the nice feature where it can set the Windows Logon Background, and since a recent Windows update and DF7 beta this image can now be multiple monitors wide.
When used on its own with any image source, this works perfectly.

Instead of using an external image source, we can also use the current Desktop Wallpaper image for the background.
The problem is that DF seems to only apply the left monitor's part to the Windows Logon, stretching it out across all three screens. This looks pretty awful.

I expect it to instead use the original image or a re-built composite image, so it more closely resembles my desktop.

OS is Windows 7; current DF Pro version installed is 7.0.0 Beta 2, which at this time is the latest one. Let me know if you need more info on my system or if this is simply a PEBKAC error, in which case I'd love to see the proper DF settings instructions for this!

Ah, good! I only became aware because of the changelog, because the issue existed before -- only in DF 6 and older it didn't stretch, I never used the feature.

It's of note that DF6 also uses only the left monitor by the way. Since on multi-monitor images the centre is usually the most usable standalone, perhaps if stretching can't be fixed, you can add an option to select which monitor image we'd like to use?