The au.streamcaching.TrimCacheWhenOverBudget value defaults to 1. This solves a potential vector for leaked memory in the streaming cache when au.streamcaching.MinimumCacheUsage is set to any value greater than zero. The leak occurs when you evict a small asset for a large asset in the LRU cache. Since this can happen many times in sequence, it results in cache usage that is much larger than your targeted max cache size.