Rather amusingly, Mars have replied to my original query.

They asked me; What was the taste difference between the two bars? Was the taste unpleasant? Have you kept any of the wrappers?

She said if I managed to get an answer to that, they could look into it for me.

It's obviously quiet at Mars Bar Towers along with at Timmy Towers

On a serious note though, if anyone agrees with 2 Mars Bars never tasting the same, let me know why and I'll pass it on to her.

Cheers
Tim

P.S It's a quiet week for me, so I'm concentrating my efforts on Mars Bars