[Ha_Loe]

I am currently using V5 on this scene, because in V4 Maxwell crashed with an out-of-memory exception, so this might be V5 related stuff. Maybe I can confirm this with V4 in a little while.

Here's the thing: All my geometry is organized in linked files (blocks), as I want to easily exchange/organize the objects I would finally gather in the scene. Some objects are variations of one and the same original file.
All is well rendering the individual objects.
Once rendering the scene, some of the textures get messed up. The materials real-scale and are applied to channel 0, no custom mapping, so I'm assuming they should be cube mapped.
In the scene render some of the textures look like plane mapped and rotated to 90deg, perpendicular to the objects surface. This does not happen always but only sometimes. Also this does not happen consitently with all the geometry. One particular polysurface exists in two seperate files and has the same material applied. Normaly only one file would screw up.

Reapplying the material in the linked file, saving and reloading the scene sometimes helped.

You can see the problem on the left vertical frame here.

The frame is an identical polysurface with same material applied, but two different linked files.

[JDHill]

My observation of recent V5 builds is that mapping is really broken at this time, and that it is counterproductive to try to debug any issues in that area currently. I will definitely look into this if you can reproduce it (hopefully with as simple a setup as possible) on V4, but not V5. One remark does stick out though:

The materials real-scale and are applied to channel 0, no custom mapping, so I'm assuming they should be cube mapped.

If the materials are real scale, then no explicit mapping, box or otherwise, should be applied; the plugin will request a suitable box mapping be created on its own. This may or may not be a factor here.