Colon in querystring getting removed?

i have a simple api that takes a prefix:
Prefix=Twin%20Peaks%3A%20The%20Missing%20Piece
unencoded = Twin Peaks: The Missing Piece
however when I get the parameter in code it is turned into

"TWIN PEAKS THE MISSING PIECE"

(without the colon)
I’m sure this sis some funky security thing happening

Works without issue for me:

image

ok thanks this must be an asp.net config thing
what is the best way to alter requestPathInvalidCharacters?
is this accessible from Hostconfig?
these are the invalid characters
[System.Configuration.ConfigurationProperty("requestPathInvalidCharacters", DefaultValue="<,>,*,%,&,:,\,?")]

This is not referenced or configurable in ServiceStack.