Champagne is carbonated, so just like any carbonated beverage it does have the potential to make a person feel gassy, especially if it is drunk quickly. There is nothing special about champagne here, rather this is just a feature of the carbonation. The solution would be to take small sips to give the gas bubbles a chance to disperse.
Also, I do not think it is likely that there is anything about champagne that could be causing unpleasant bowel movements. This sounds a lot more like what people describe when drinking any form of alcohol; it is quite common for people to say that they have different bowel movements after drinking the night before. Sometimes, as in the case of heavy dark beer, this may actually have something to do with the carbohydrates and other substances in the beer. However, in the case of champagne I think it is much more likely to have something to do with whatever different types of foods you tend to be eating in the same occasions in which you drink champagne.
If the symptoms persist or worsen, you can talk to your doctor
. Otherwise, just make sure to watch carefully what you eat and drink.