You never look at just the last 12 months. You need to be looking at the last 5 years at least. If their returns have been good over the past 5 years and you have been happy with that,what's the problem. Every fund will have a bad year every so often. The trick is what they do during the down turn.
Last time I checked we were in the middle of a world wide downturn. Every fund is down unless your 100% in cash. If your returns have historically been good, then this is the perfect time to be putting extra money in. It's like a huge sale, everything at reduced prices. If you have lost 21% over the past 12 months now is not the time to be selling. Your loss is only on paper and will only become reality if you do sell.
I don't know the first thing about TAIST, maybe it is a dog? Get some good professional advice before you make it even worse.