It seems if it’s forgotten to behave like a texture instead of an image. Was the jpeg inserted as image, first?
How did you applied it to the other faces? was it grouped already, or did you group it afterwards?
Can you upload an example file where this is happening?
It might be related to this bug:
Here’s how to reproduce:
Open a new (blanc) file.
Import an image and draw an edge.
Group both entities.
Draw a face, choose the paintbucket tool.
Sample from the image Group and apply to the new drawn face.
Check the 'In Model collection ’ of the Materials panel.
Set Face style to ‘Hidden Line’