This issue happens as SDL Tridion 2013 SP1 was targeting .NET 4.0, and Web 8 targets 4.5.2. As a result, binary URLs with below special characters will be encoded.
: / ? # [ ] @ ! $ & ' ( ) * + , ; =
For a more detailed description of the change in behavior when targeting the Microsoft 4.5 .Net Framework, see below documentation link (Known Issues in Content Delivery)
http://docs.sdl.com/LiveContent/content/en-US/SDL%20Web-v1/GUID-DA9B138D-3710-424E-AEE7-9105556B33C9