In which cases does the Undo buffer gets stored here - %temp%\Bentley\MicroStation\10.0.0\Undo? There ar zero size files most of the time.
Is it possible to set that Undo buffer is stored in file cache and not to delete them on exit?
Although there are tmp files storing the command operation to undo within this location it has only been a temporary undo list for the current session of MicroStation. This has been like this since V8 was released as MS/J used to have a configuration variable MS_UNDO that was able to define how mush memory to allocate to the buffer.
https://communities.bentley.com/communities/other_communities/askinga/w/askinga/1053/the-types-of-configuration-variables
This operation is usually require to go back to a previous version of the file you have been working on. It is recommended in this circumstance that Design History is used.
https://communities.bentley.com/products/microstation/w/microstation__wiki/2932/working-with-design-history-in-microstation-v8-cs
RegardsAndrew BellTechnical SupportBentley Systems