Tascam us-1800 and Mac--Sleep issue

My tascam us-1800 seems to work just fine until my Mac has gone into sleep mode a couple of times. I used to think it was because I had left Reaper open when it went to sleep, but now the interface just sort of disappears until I restart the computer.
I'm wondering too if these interfaces are really intended to be left on indefinitely, as if it's a glorified soundcard, as some people have said. It seems like anything left on for weeks on end is likely to die sooner anyway. This is my first audio interface, so I don't know if this is typical behavior, peculiar to Tascam hardware, or a sign of something wrong. For the record--it's always done this since I've had it, which is about as long as I've had my Mac (just under a year).