css file reverts to one saved on computer – Please

I have this very strange problem, I have posted a query on Friday but didn’t get an answer. I think it will sound rather goofy, but it is real and annoying. I have updated my css with new layout features (such as the greyish background color, the borders, etc), for the first time about 5 days ago. On Friday, I noticed that my css reverted to a very old version (but not the standard wp-layout, I use another file, wp-layout-kit). I am sure I didn’t do anything, nor did I update my site in these days. I didn’t have the new version backed up, but I have it more or less restored it from memory. I also realised that the css reverted to the old .css I had on the office computer. I checked the site right now and I see that the reversal happened again. I didn’t surf or otherwise use my computer since Friday.
I am mystified and very annoyed. Are the wordpress files tied to files on the office computer? Please, if you have any ideas, help me out. I will probably delete the old file in the library when I get there, but it should not happen.
And it is not a cache problem. The old file appears when I am editing it in WordPress.
Thanks!
Renee
http://glosses.net