i have just pointed out 6.0.0-beta3/6.x but it must be same in 1.5.x too ,afaik "?" is not considered part of querystring ,"?" is considered separator see http://tools.ietf.org/html/rfc3986#section-3
this method is used in Url#toString() too which can be easily fixed but it may be used at other places too so i don't know if removing "?" will break things now.
so how things break currently
decodeparameters will considered first key to be "?key"
so may be requestutils#decodeparameters method should strip away "?" if it's present in the query string before populating pageparameters