NetcdfFileWriteable strangeness on attempted file overwrite

I'm not at all sure if this is intended behavior of the Java netcdf API 
for the NetcdfFileWriteable class, so I am not claiming this to be a 
bug, it just seems strange to me.  Using nc2.2, OS is Redhat Enterprise 
Linux, JDK is Sun's 1.4.2_05...

I am using the NetcdfFileWriteable class as such

NetcdfFileWriteable ncw = new NetcdfFileWriteable( "foo.nc", b );
add dims, vars
ncw.create();
write data
ncw.flush();
ncw.close();

where boolean b = true or false, makes no difference to the following 
observed behavior.

Now, I want my app to hose any existing file foo.nc, i.e. my app knows 
what needs to be written to foo.nc, and any previous contents are 
irrelevant.  Depending on the config of my app, different amounts of 
data are intended to be written to foo.nc.  My app always writes all of 
the data for all variables defined, so no 'fill' is required.

Now, the strange part is that if foo.nc exists and I run my app, the 
contents of foo.nc will only change if the total size of the new dataset 
in bytes is larger than the existing size of the file foo.nc.  If the 
app intends to write a smaller total number of bytes to foo.nc than is 
currently on the disk, say to define fewer variables than a previous 
run, then the new contents are not written.

Even more strangely, no matter if the file contents are or are not 
updated, the timestamp (file modification time on Unix??) of the file is 
updated unconditionally.

So, in short, my app will have to remove the file if it exists to be 
sure of the correct final contents of the file??

As I said, maybe this is as it all should be.  If so, are there docs to 
show this?  The javadoc comments for the class suggest to me that what I 
want to happen, should happen, but it isn't happening ;)

Any clarifications appreciated

Stuart