I checked with dotPeek and for the unobfuscated assembly it shows one reference to:
mscorlib, Version=188.8.131.52, Culture=neutral, PublicKeyToken=7cec85d7bea7798e
When I expand that reference, I get the mscorlib assembly with the WindowsPhone71 profile.
For the obfuscated assembly, it references the same mscorlib but also System.Windows.Browser (System.Windows.Browser, Version=184.108.40.206, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
Can you give me a pointer on what compiler settings might be causing this problem - I'm happy to try things out, but I am very confused as to why this is happening at all with an empty, unmodified project and I'm not sure where to start with poking around at compiler settings.