Default vendors are invisible. New vendors (modified with patterns) are visible.

I can see the vendor names for the default vendors, but the vendor is invisible. I can hover over the area where the vendor should be and the cursor turns green and can interact with the vendor. The new patterns applied to vendors are visible and act normally. This occurs in multiple POTs and my own POT.

 

This btw is version 733 with the invisable vendors

 

How do I put the pattern on a vendor, anyway?

Never mind... I found out how to apply the pattern to the vendor.

Spoiler: Press to see how to apply the pattern

Pick up the vendor.
Take the vendor to an alchemy table.
Place the vendor on the alchemy table.
Place the pattern on the alchemy table.
Place 5 mandrake on the alchemy table.
The Craft button should light up.
Press Craft.

Or, just search for 'modifications' in your alchemy recipe book and double click that. Then click craft.