I was in Niagara Falls, Canadian side, for one day, tried to reenter the US with temporary I-551 stamped on my valid Refugee Travel Document. The officer at the border looked like he had never seen my document before, nor had he seen an I-551 stamp. He flipped and opened every page, scanned it a few times, then called two different people, to one of whom I overheard him saying: "You're an immigration guru right?"
Got sent to secondary, where I had to ask someone to speed up my case since I had a plane to catch from Buffalo. He looks at my document and says "I don't know what you're doing here" stamps it and sends me on my way.
Point of the matter, always be prepared for a meeting with a less than stellar USCIS employee.