Stug IV, Super Hellcat, etc... are not premium tanks {{v.premium}}, they are special reward/giveaway {{v.special}}.
They have premium characteristics, but not marked as premium.
So replace {{v.premium}}.png with {{v.premium|{{v.special}}}}.png and make copy of your premium.png image as special.png
Also since 1.10 i have font glitching on my config, but can't be bothered to investigate.
Just load different page (example:techtree) and go back to hangar and its back to normal.