From the Crypt::Blowfish man page:

In fact, if you have any intentions of encrypting more than eight bytes of data with this, or any other block cipher, you're going to need some type of block chaining help. Crypt::CBC tends to be very good at this. If you're not going to encrypt more than eight bytes, your data must be exactly eight bytes long.

So, your data isn't encrypted properly. Crypt::Blowfish only does its work on eight bytes a time -- a block. It's just that you can't tell until you go to decrypt it.

Crypt::CBC is a front-end to encryption modules that does the proper chaining, handles byte padding,etc. It's well documented.