Last year, we stopped at a little creek to fill up. My buddy had his Katyden hiker pro and I had my MSR. When we got done pumping, my buddy said that his tasted pretty bad and asked if I would try it to verify. Well, I had taking a couple swigs off of mine and it tasted fine so I took a big pull off his and it tasted like straight cow pee. After about five minutes of gagging and dry heaving, we dumped our water and went to the next creek to fill up. My water tasted fine but i still dumped it.
Case in point, i believe my ceramic filter took the bad taste out while his Katyden didn't. Not sure if others have had similar results but that was mine.