Post date: Mar 29, 2012 3:8:1 PM
It appears that there is a problem with certain characters in the names of uploaded files (attachments), such as files containing a model. The symptom is that the file will not appear in the list of files attached to a page, even though it is possible to see that the file has been uploaded when you look at "Recent site activity", and indeed to access the file there.
The particular characters which caused the problem were round brackets (...), but the advice is to avoid all 'special' characters in file names. Use only a-z, A-Z, 0-9 and the space and underscore (_) characters, and you should be OK.