You got me there Lyndel...
Using Powerzip & not understanding why there should be comments...

Here's what I did this time:

1. Renamed pronto.pcf to pronto.zip
2. Unzipped to folder
3. Folder and xml file present at root, nothing else
4. Did NOT change the xml file this time
5. Rezipped the folder and the xml to pronto.zip
6. Renamed to pronto.pcf
7. PENG says it's corrupted

IMO this is exactly the same pcf I started with, unless I am missing something...
I must be doing SOMETHING wrong, but what!