JJ,
Your files are probably still there. Use "explorer" and you may see the "exploded" files _a, _j etc. Use the pull down to select "pre 5.0" files and you can open them and then will be rezipped to .CAESAR II. You can also look in your .temp dir or just do a search on your computer before you recode a large file that has really not disappeared.
This also happens sometimes (or did in the past) when you include a piping file. The included file was "exploded" and remains looking like a pre-5.0 format.
Just some thoughts.
_________________________
Bob Zimmerman, P.E.
Vice President of The Piping Stress International Association (The PSI)