Stripping HTML from the message body returned by a rest call

That's odd. I don't recall seeing anything like that before. How many characters is the string you're dealing with?

There's actually a newer method for truncating strings that you may want to check out to see if it works better for you:

http://lithosphere.lithium.com/t5/support-knowledge-base/Character-truncation-variables/ta-p/38324