Weird Missing Media Thing on PT LE 6.1

[soundbird]

Okay this is a bit of a strange one!
I am using LE for the first time as I'm usually a TDM girl so I don't know if this is some weird known bug or something.....
I have been tracklaying some FX and at some point some random FX have disappeared totally, both from the timeline and from the AudioFiles folder. These media files are nowhere to be seen or found on my system!
The only time that I have deleted anything is when I selected and deleted unused media from the regions list.
It is quite a random problem and appears to only affect two particular tracks and then not all of the track. The only other thing that these missing media clips might have in common is that they were 'bitty' edited clips so I duplicated the clips using Audiosuite dupe so that they would become one clip and this also created brand new media files. However I was doing the same thing the day before on different tracks and they are all okay the media is new and in the AudioFiles folder.
Any ideas ?..........
I am now having to redo all that was lost but in the meantime I don't want it to happen again.
Cheers
Sarah