random zero clip length

[pomonabill220]

Hi all.
I am running 5.2.3.2 x64 version in direct to disk mode.
Randomly I get clips that are zero length on random cameras. There doesn't seem to be any pattern or situation when these files are create and they don't seem to be created, but the thumbnail is created.
When I click to display the zero length file, I get "Sorry the file cannot be found" popup, but the thumbnail is there with the time, just 0 seconds long.
When I repair/regenerate the database, the zero length files are no longer listed.
When I compact/repair they are still there with a 1 second length.
When I "run maintenance" (what is the difference also), they are still there also.
What could be doing this? and where is BI getting the thumbnail from is the file doesn't exist?