Isn't this just because LTC rounds tend to take a long time? I've seen this kind of thing but I always get paid out eventually when the pool finds a block.
Problem is the switching. If another coin becomes more profitable while mining LTC the multipool switches and as far I understand at that moment you lose alle your LTC shares if the block hasn't finished yet.
It takes 24 hours to lose all your shares after the switch to another coin. There are some people who mine LTC directly and not on multiport. So, if a block is found in the next 24 hours (after your last share), you would still get your reward.