If you look for the IL-code of this string switch code, you can find some il instruction for string interning (convert string to reference) to speed up string comparison (comparing by reference) in the switch, this trick of compiler does functioning of encryption on this portion of code incorrect. This problem related only for string switches.
To avoid this problem replace string swiches by usual if-else-elseif condition statements or you can use switches with string hashecode comparison:
switch(strVar.GetHashCode() )
{
case "/debug".GetHashCode():
_debugmode = true;
break;
case "/dummy".GetHashCode():
_debugmode = false;
break;
}