m210.dump() does not dump everything if used other than stdout as a destination

I am not quite sure what the problem is, and I was wondering whether there is a way to debug it. Initially, I tried to save notes to RAM from python, but as far as I see, this might not be possible, because the library function m210_dev_download_notes requires a file number. I am sure this could be fooled somehow, but perhaps it is not so important. However, when I tried to save notes to disc from a python session, I realised that not everything is read from the device. If I do this on the command line

m210 dump > fujitsu.pegvf

then the file size is 233802, and all data are transferred. However, if I do this from a python session

>>> import m210
>>> a = open('test.pegvf', 'wb')
>>> m210.dump(a)
>>> a.close()

then the file size is only 233472, and a chunk from the last page seems to be missing. Is there something that I should do in order to get the whole content of the memory? As a temporary measure, I could issue a system call, but I just don't see why that is different. After all, the command line and the python module calls the very same library.
Thanks,
Zoltán