Every time I edit a sheet, some of the data from my latest changes disappears.

I originally uploaded a multi-sheet Excel spreadsheet which included spanned cells and borders.  The first image shows what it looked like after I saved the spreadsheet.

After waiting a couple of minutes (until my firefox browser's "working" indicator stopped spinning) I switched to another sheet and then switched back. All the data was there.  I then closed the browser.  I came back about 30 minutes later to verify that the data was there.  However, as you can see in the image below, one box was empty (circled in green).

The red dots on the image below indicate which data items I added to the sheet on a previous date and the blue dots indicate which of those data items had disappeared the enxt time I opened it.

Can someone tell me why this is happening?  Does it have something to do with the merged cells or borders?  I have just started using the Zoho products and am very impressed, but I can't see myself using a sheet tool such as this if the data randomly disappears.

Thanks,

Tracy