C# HttpPostedFileBase.ContentType fails one string comparison, passes another

Question

I'm trying to compare the content type of an HttpPostedFileBase against an array of acceptable types, and I'm encountering some genuinely odd behaviour.

array.Contains() can't find the string, but if I iterate over the collection and compare each entry to the string, it gets a match.

Here's my code:

string[] acceptable = new string[]{ 
    "text/comma-separated-values", 
    "text/csv",
    "text/anytext",
    "application/csv",
    "application/excel",
    "application/octet-stream",
    "application/vnd.ms-excel",
    "application/vnd.msexcel"
};

string type = model.file.ContentType.ToLower().Trim();

string err = "acceptable.Contains(type) = " + 
             (acceptable.Contains(type) ? "true" : "false");

err += "<br/><br/>";

foreach (string s in acceptable)
{
    if (s == type)
        err += "but " + type + " is definitely in the string array!"; 
}

The code above outputs the following

acceptable.Contains(type) = false    

but application/octet-stream is definitely present in the string array!

If I copy and paste the printed value of file.ContentType into a string variable and run the comparison, it works fine. It only fails when reading the value directly from HttpPostedFileBase.ContentType, which is of type System.String by the way.