URL encoding doesn't work for "&&"

When adding the following property: passwd = 1234&567 to an HTTP Request step. The GET request does not URL-encode the "&" which breaks the query.

Raw request =
GET http://xxx.xxx.com/cat6/Login?passwd=12 ... e=testuser HTTP/1.1
Accept-Encoding: gzip,deflate

At first I thought that maybe I needed to encode the property valuenmyself but there is some level of URL encoding happening when using other characters like this: passwd = 12345#67

The GET looks like this:
GET http://xxx.xxx.com/cat6/Login?passwd=12 ... e=testuser HTTP/1.1
Accept-Encoding: gzip,deflate

I'm not sure why # would get encoded to %23 and not &. FYI, "&" is not the only special character that does not get encoded, @ does not either and I'm assuming there's others too!