I cannot believe this has not been fixed by now!!!!
The issue seems to be that if the user saves an assembly and this assembly has parts or sub assemblies that need rebuilding and also saving, solidworks just bypasses the process to save a bitmap preview image.
The only way, I can see,is for the user to troll through the whole main assembly and open each part/sub assembly and save every one individually, so all parts/sub assemblies are up to date, then save the main assembly.
This is all fine, until a change is made on a part, say in a sub assembly, then that part is immediately out of date and again and those parts/subassemblies (all below the main assembly) loose their preview when main assembly is saved.
What a screwup!!!!!!!!!!!!!
This preview, surely, is a fundamental part of the usability of the program (or indeed any windows program).
When the user is sifting through many slightly similar items with no preview this becomes a PITA.
Attached screen cap shows the problem.
The part on the left was edited & changed within the main assembly (preview image on right).
Now the preview bitmap image has winked out and all there is shown is a useless icon.
I have tried the past suggestions etc that have appeared on the forums in relation to the preview issues, none seem to address or fix the issue. It seems the only way it can be fixed is by the fundamental code within the SW program.
And yes I have been into view options on windows explorerer and made sure "always show icons, never thumbnails" is UNCHECKED.
Windows 7 SP1
SW 2011 SP4
Graphics Quadro FX1800 with latest SW recommended drivers.