This one seemed to be an intermittent error until I nailed it down.  No sign 
of this issue in bugtracker to date.

(1) Demo of 'inactive' formula bar behaviour:

Run CALC and ensure that the formula bar is visible (if not then activate it, 
close CALC, reopen).  Do not open an existing spreadsheet, just let CALC open 
to a blank spreadsheet.

Before doing anything else, open a recently used spreadsheet or browse to a 
file and open it.  Click on any non-blank cell.  Notice that the formula bar 
remains blank, even though it should be displaying the formula or value in the 
active cell.

(2) Demo of formula bar behaving normally:

Shutdown CALC.  Browse to the file you used in (1) above.  Double-click on it 
to open it in CALC. Click on any non-blank cell.  Notice that the formula bar 
is displaying the formula or value in the active cell.

OR

Let CALC open to a blank spreadsheet.  Type in any number in the active cell. 
Notice that the formula bar is displaying the formula or value in the active 
cell.

Let me know if you cannot reproduce this yourselves and I'll investigate 
further, link some screenshots, etc.

Regards,
Andrew Ferguson