When you are using System Monitor to observe DNS memory usage, the DatabaseNodeMemory counter steadily increases over time, indicating a possible memory leak.
When DNS node memory is released, the DatabaseNodeMemory counter is increased instead of decreased.
Use the Private Bytes counter for Dns.exe to monitor DNS memory usage. This counter reports total memory usage for the DNS process, including code and DNS data.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.