Have the same issue, also experimented a lot without success unfortunately. Looks like token values are automatically url safe encoded making them unsuitable for complete url's.
See the docs here for more info: http://docs.splunk.com/Documentation/Splunk/6.2.1/Viz/tokens#Token_filters
Where they mention:
Filter=URL format: $token_name|u$
Description=Ensures that the token value is valid to use as a URL. Token values for the element < LINK > use this filter by default.
So looks like this behaviour is by design and cannot by overwritten AFAIK.
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