There are a couple of long-term bugs with 12.04 and bluetooth transfers. I have a similar problem with two older Nokia Symbian phones.
My workaround is to install obexfs and mount the phones to a folder in my home directory.
Unmount it with
obexfs -b xx:xx:xx:xx:xx:xx <folder>
(Replace xx:xx:xx:xx:xx:xx with the identifier for the phone/tablet.)
I've found that it gives a good, solid connection. I can drag and drop files from one device to the other in the usual way with no problems. I've even had both the phones mounted at once (to different folders) and transferred files from one to the other.
fusermount -u <folder>