Unity version:
Version 2019.3.0a12 (d958c49352ef)
Happens on versions as early as 2019.1.14f1
Repro steps:
1. Create a new project
2. Add LWRP/Universal RP and Shadergraph
3. Create a Universal/LWRP Pipeline asset and set it as the graphics pipeline in project settings
4. Create a new shadergraph
5. Recreate the shadergraph shown in the attached image, using any texture that's not a flat color (you can use the default particle texture if you don't want to get any new textures to put in your project)

Expected result: the texture mirrors once, and clamps everywhere else, leading to 4 "copies" of the texture and clamped behavior elsewhere
Actual result: the texture mirrors over the entirety of UV space, as shown in the attached image