If the pool is designed to always mine the most profitable coin and the coin that the profitability is based on is litecoin then in theory we should never go below litecoins profitability as when litecoin is the most profitable then we are mining that
Again, that's just variance. Sometimes you find more blocks, sometimes you don't find any for a while. Calculated profitability is just a hypothetical average over an infinite time span.
+1. If you think that going beyond the 'ideal' profitability of LTC mining means there is something wrong, you just need to study the economics and probability of cryptocurrency a bit longer