So if you use fast skin change and switch from a 720 to a 1080 skin that can happen. Enigma restart should solve it.
My debug shows the resolve list and the selected file for that image.
Code:
< 187.5118> 23:58:39.3951 [Skin] Processing screen 'Volume', position=(1425, 15), size=(480 x 102) for module 'Volume'.
< 187.5132> 23:58:39.3964 resolveList ['/etc/enigma2/', '/usr/share/enigma2/ViX-Night-1080', '/usr/share/enigma2/skin_fallback_1080', '/usr/share/enigma2/skin_default', '/usr/share/enigma2/']
< 187.5135> 23:58:39.3967 file /usr/share/enigma2/skin_fallback_1080/screens/volume_up.png
In the case of the EPG marker line, the graphic is wrong... still scaled for 720, so needs fixing.