Having UV channel beyond 2 creates broken lightmap behavior

this mesh bench_05

Has a uv on channel 8
this is unused by me AT ALL,
but upon import unreal treats it like uv 3
and more than that, trying to bakea lightmap off of proper uv 1 (second channel) becomes impossible
as lightmapper produces this broken pattern

http://i.imgur.com/Inxbk9V.png

You can read the thread

Im mad there because people who have no idea what they are talking about keep parroting about padding which is obviously unrelated to issue.

The SOLUTION however was to open blender and remove that additional uv channel, after what everthing went back to normal.

Hi samb -

Thank you for your report, to effectively test this can you upload a copy of the base color texture you are using? I agree absolutely not a padding issue. If you would like to keep it private you can upload it to me directly via the Engine Forums.

As far as the condensing of the UV channels, this is actually done on FBX export from the modeling programs, and not on engine import. Your FBX will open in Maya for me with UV 1,2,3.

Thank You

Eric Ketchum

http://i.imgur.com/8ef8AaJ.jpg

Ty for responce i didnt know that about exporter.
here is low res texture, is it fine for testing?

Hi Samb -

With your texture and following these import settings I was able to get your asset in with no UV issues.

Import SM without Material and Textures and With Generate Lightmap not checked true.

The Asset comes in with UV0 (Texture Layout), UV1 (Lightmap Layout) and UV2 (?Junk Layout)

Applying a Material using the texture from above onto the SM results in a perfect bench asset.

Thank You -

Eric Ketchum

Ok so on your side on new project there is no issue, but i had it, what was it then? Was i the cache or something? Why it bugged like that on my side?

[QUOTE=jonimake;270085]I used to get similar problems in UDK. Deleting the lightmass swarm cache helped usually. You could try the same.
The cache can be found in: %localappdata%\UnrealEngine\4.7\Saved\Swarm\SwarmCache[/QUOTE]

I tried all index.destination combination with the same result of tiled broken pattern, after test by Erik on answer hub im mostly certain the problem was in cache.
I can’t test it right now but the way i though i “fixed” it by deleting uv channel was actually that i Imported new mesh, with new uv, not REimported,
which means a new cache for it was built, which means i falsly assumed that was the solution.
Despite there is a way to solve this issue like in my case by importing new model, or removing the cache,
that doesn’t change the fact that i experienced a bug, in which the lightmap got literally stuck on that model in that project.
Due to what that could happen?