Helo HomerJ,
Generally the expected outcome in the instances you have described are the appearance of a fuse exceeded or size limitation error presented within a pop up box presented to the user during the attempted action. Depending on the method being used (user gui, email attachment, etc) then the attempt4ed upload may just complete without notification and create an attachment with a 0KB size. This is a normal response when the sizing of the attachment is greater than the available storage free space. What it seems you are experiencing within the normal operational design.
You may want to see the following post: http://eyeontesting.com/questions/17240/limiting-attachment-size-in-alm.html on ways to limit the sizing of attachments uploaded to lessen the chance of this further occurring in the future.
Dan