At job, I use CAO software called Catia to create drawings.
I activate "Use shell image extraction for formats Opus does not understand" to show thumbnails.
When i generate thumbnails, Dopus increase memory usage but never set free.
For example, if i generate thumbs, then quit thumbnail to list mode, then thumbnail mode again, memory usage grow up again.
when opus set memory free ?
Does the same thing happen in Explorer?
It's likely that there is a memory leak in the 3rd party shell extension DLL that generates the thumbnails for both Opus and Explorer.
Thumbnails remain cached in memory when you change to other modes. It's worth checking whether the memory is freed when you close the window or navigate to another folder.
Of course, if the memory usage doubles every time you switch back to thumbnails mode, or it's using 500meg and there are only a few files, then something is obviously wrong and it's probably a memory leak in the shell extension which creates the thumbnails.
Same folder in Explorer, 53mb 
If i close all Lister, memory decreased
How many images are in the folder? If you've got dynamic thumbnail sizing on, and all the thumbnails have been generated, then Opus will be caching 256x256x32 (I think) images per file which can add up to a lot with thousands of files.
~300 files and it's not images (so no resizable)... it's preview off CAO 3D part
Thumbnails are always images. If dynamic sizing is on then Opus will request a 256x256 image from whatever generates the thumbnail.
That said, if there are only about 300 files then thumbnail caching doesn't explain why so much memory is being used.
256x256x32/8 = 262144 bytes per image
Much less than what you're seeing. Hmm.
Maybe there's an incompatibility between the Catia shell extension and Opus. Is there a trial version of Catia that could be used to test with?
It might be worth setting Opus to only use 1 thumbnail thread in case using multiple threads is part of the conflict.
I don't think there is trial version of Catia http://www.3ds.com/products/catia/catia-discovery/
it's not 256x256 because i can reduce size but max size is 128.
I notice strange, there is no problem with standard version (on PC) but problem in USB.
But if i use 2 threads, it's better.
Does toggling thumbnail caching have any effect? That might be the difference between the normal install and the USB install.