Cosmic Ray destroys my work

This is my shell history

  484  gnutar cfz MyProject.tgz MyProject
  ....
  493  rm -rf MyProject
  494  gnutar xfz MyProject.tgz 
  495  cd MyProject
  496  open MyProject.xcodeproj
  497  cd ..

then I typed

$ rm -rf MyProject ; !gn

which expanded to

rm -rf MyProject ; gnutar cfz MyProject.tgz MyProject

no kidding!

$ gnutar xfz MyProject.tgz MyProject
gnutar: MyProject: Not found in archive
gnutar: Error exit delayed from previous errors

What do you think ? A cosmic ray, a bug in bash or a faulty RAM ? I went with faulty RAM and installed the 12 GB I had lying around here and I always forgot to install. Lazyness is not always a virtue....