Observed in Calc with xls file;  I did not look at other components.

If a file is opened in read-write mode (the default), then toggled to read-only (using the 'edit file' button, the file is still kept open (now apparently in read-only mode) (based on my observations using sysinternals process explorer).  As far as I can tell, there is no need to keep a read-only mode file open once it has been read in.  However, there is a good reason to close it once it has been read in.  Namely, Windows 7 (and no doubt later versions) will not permit a machine to sleep if it has a file opened across the network.

Meanwhile, it appears that if a file is initially opened in read-only mode (by checking the read-only check box in the open dialog), then the file is closed once it has been opened and read.

If my observations are correct, then this is inconsistent behavior, and when a file is toggled from read-write to read-only, the file should then be closed.
              
Operating System: Windows 7
Version: 4.2.5.2 release