I decided to run 'emerge --fetchonly openoffice-bin' and leave the system running while I was sleeping. When I woke up it was still downloading (my connection is slow, but it shouldn't take that long to download). I noticed it was saving it with extension .tar.gz.3 but I didn't mind about it. When it finished, it just started again wit extension .tar.gz.4, so I canceled it, checked /usr/portage/distfiles/ and found a lovely surprise: the .tar.gz was incomplete, but .tar.gz.1, .tar.gz.2 and .tar.gz.3 were all complete with the same md5sum (oh, and an incomplete .tar.gz.4). I guess it just failed in the first try and was unable to resume, but after every successful download it didn't rename it, the system tried to check the file again, but since it was incomplete it started another download and so on.
emerge --info missing, assuming dupe. *** This bug has been marked as a duplicate of 145601 ***