Assigning anything to a Perspective property (session or component) turns anything not directly supported by JSON into a JSONified substitute. Completely breaking anything like byte arrays or other complex jython objects.
My free Integration Toolkit module offers sessionVarMap(), pageVarMap() and viewVarMap() as an alternate storage location for jython objects that won't destroy their original form.
(There are alternatives using system.util.getGlobals(), but there be dragons.)