Base64 problem with jQuery Async Treeview

Question

In my ASP.NET MVC app I'm using jQuery Treeview with Async node expansion to build a tree of Active Directory objects. I'm encoding id's of each node with Base64 due to request length issue. For example in response for http://devel.local:49210/Domain/LeafExpand?root=source I get the following:

[{"text":"DC=anusiewicz,DC=pl","id":"REM9YW51c2lld2ljeixEQz1wbA==","expanded":true,"children":[{"text":"CN=Builtin,DC=anusiewicz,DC=pl","id":"Q049QnVpbHRpbixEQz1hbnVzaWV3aWN6LERDPXBs","hasChildren":true},... etc.

but

in some cases after selecting a node that has children jQuery instead of sending request like this:

http://devel.local:49210/Domain/ShowProperties/Q049R3J1cGEgeiByZXBsaWthY2oIGhhc2UIG5hIGtvbnRyb2xlcmFjaCBST0RDLENOPVVzZXJzLERDPWFudXNpZXdpY3osREM9cGw=

sends it like that:

http://devel.local:49210/Domain/ShowProperties/Q049R3J1cGEgeiByZXBsaWthY2o/IGhhc2U/IG5hIGtvbnRyb2xlcmFjaCBST0RDLENOPVVzZXJzLERDPWFudXNpZXdpY3osREM9cGw=

Additional '/' causes web server to generate 404 error. Why is this happening?