It says in the Gemorah Pesachim Daf 115a:
אמר רבינא אמר לי רב משרשיא בריה דרב נתן הכי אמר הלל משמיה דגמרא לא ניכרוך איניש מצה ומרור בהדי הדדי וניכול משום דסבירא לן מצה בזמן הזה דאורייתא ומרור דרבנן ואתי מרור דרבנן ומבטיל ליה למצה דאורייתא
that a person shouldn't eat matzah and maror together b'zman ha'zeh (nowadays) since the taste of the maror will be mvatel (cancel) the taste of the matzah. The chiyuv (requirement) of maror which is m'drabbanan will be m'vatel (in taste) that of the chiyuv of matzah that is m'doraisa.
However, the Gemorah says on Daf 115b:
אמר רבא בלע מצה יצא בלע מרור לא יצא
that if one swallows matzah whole they are yotzee (however if they swallow maror whole they are not yotzee).
We see from the Gemorah on Daf 115a that one needs to taste the matzah, so why then does the Gemorah say on Daf 115b that you would be yotzee in a case of swallowing where you seemingly wouldn't taste the matzah (wee this idea from the fact that maror you aren't yotzee.) Or perhaps the question could be asked the other way. It says in Daf 115b that if you swallow the matzah you are yotzee (we see then that you don't need to be feel the taste.) However from the Gemorah on Daf 115a it would seem that you do (since the taste of the maror will be m'vatel the taste of the matzah.) How can this contradiction be addressed? Are there any maforshim that speak about this?