A little water sitting below the filter is normal. It’s possible that there isn’t a check valve which can cause it or the way the older Bosch dishwashers work, they don’t completely dry, so a small amount of water can gather. That said, a rinse cycle with vinegar won’t hurt anything. The only downside is this small amount of water below the filter can start to smell if the dishwasher is used infrequently. If that’s the case, leave the dishwasher cracked open to dry and clean the filter. For a very small amount of water, below the filter, I wouldn’t pull the machine to check for clogs.