Surface of high-order DG function includes internal surfaces

I have been saving some functions as discontinuous linear or quadratic functions and while postprocessing I realised that the mesh “surfaces” include the facets, aka the boundaries between cells.
For example in the screenshot below

you can see that the ExtractSurface filter, on the right, keeps the boundaries between cells.

This makes it very hard to visualise data sometimes, is there a way to fix this? Should I file a bug report?

Example data: (9.2 KB)

This topic is similar to Opacity for high order function with the exception that I don’t have this problem with continuous functions, only with discontinuous functions.