LibreOffice Portable Version 3.6.1.2 (Build ID: e29a214) Calc Cell Value Display issue

Not sure what is going on, and I couldn't re-create it to take a screenshot, but ...

Essentially - I have a speadsheet with a numeric value in a cell. I change the value in the cell and hit Entry. The cell displays as blank, even though the updated value is shown on the address bar and used in subsequent cells.

I can click on other cells and the value is not displayed in the affected cell - however, I can save the worksheet and/or change the format of the cell to currency and back and then it does display.

The files are saved as .xls files, if that makes a difference.

I have run into the issue on two different PC's, so I don't think it is a display driver issue, but I used 3.5 (3.5.4?) previously with the same files with no issues.

Ideas?