Winzip password collision

I created this zip file for a word guessing contest at ForumWarz, using a strong password, "5be890c219b0a837600e5fbb7ae8a2505be890c219b0a837600e5fbb7ae8a250" (not insanely strong but I guess that's strong enough for an average user). But it got cracked easily using AZPR with a brute-force attack.

It turned out that you can unzip the file with a much shorter password "tdc4Dl" too.

Surprised? I knew that zip protection was insecure but never thought it was that terrible.

This paper has some more information about zip encryption weaknesses, but I'm too lazy to read something that long. Maybe rhican can enlighten me :)