Joomla latest and VM latest.
To replicate the bug:
1)Create two Vendors.
2)Go to your current Shop/Vendor and try to modify "invoicing" style. Save and then press "Here" to see the preview.
3)You'll see that the "invoicing" doesn't update with the style changes.
Basically I discovered that you have to change the style in the other vendor, so it gets reflected in your current one.
If you need a backup or something, please tell me and I will share it with you.
I think you got mixed up with the different vendors.
Yeah. Probably. Sadly there is really few documentation regarding "multi-vendor" usage in the documentation :(