http://www.livestrong.com/article/333816-caffeine-stomach-ulcers/
http://www.healthy.net/Health/Article/Effects_of_Caffeine_and_Coffee_on_Heartburn_Acid_Reflux_Ulcers_and_GERD/2396
Here are a couple of websites that explain how in some cases caffeine is associated with ulcers. I am sure it is just in extreme cases but if you already experience reflux or IBS ( like I do), it might be best to stay away from it.