Is there a bug in the 6610 operator logos?

We run a service that sends Operator Logos on request by text message. We have 4 test logos, that work fine when requested from any UK network on most Nokia phones. However one of the 4 logos fails on our new 6610. It says "Operator Logo Received", but instead of showing the image, it shows a small icon of a musical note. The exact same image shows fine on my 3110. All other images show fine on the 6610.

To run a test, in the UK, text LOGO DEMO2 to 84880. This is the one that fails on the 6610 but not the 3110.