Ps CS6 Problem: unable to prevent uncompressed compatibility image being saved in 32-bpc docs

Question

Ps CS6
OS X 10.6.8
There seems always to be an uncompressed compatibility image in 32-bit PSD and PSB, and in 32-bit layered TIFF. That's regardless of Maximum Compatibility being disabled when saving.
If Maximum Compatibility is enabled, there correctly is an uncompressed composite in the file.
If Maximum Compatibility is disabled, there's an overhead equivalent to an uncompressed image with the document's size. I reckon the all-white compatibility image is uncompressed! If any image should be compressed, that surely is it. What a ridiculous waste of storage space. An unnecessary consumption of hundreds of MB per document in many cases.
This uncompressed compatibility image would explain why an embedded 32-bit PSB which stores the IBL of a 3D Layer consumes the enormous storage of a large uncompressed 32-bit image despite it being compressible to a few hundred KB.
If I've missed some switch to prevent this waste of storage, please point me to it. Otherwise, please employ compression when appropriate.

Answer 1

That is correct - without that, many other applications fail to read the file.
We think we've got a way to compress even the solid color data in 32 bit/channel, but it wasn't as straightforward as it sounds (floating point is tricky).