Hi,
If the memory leaks when native API is invoked, and does not leak when the native API is invoked, then either the native API is used incorrectly, or there is a memory leak issue in the native API.
Unfortunately, with no access to your code or your application, I'm afraid we can't help you with this unless you provide a way for us to reproduce the issue.
In Rebex libraries, we call lot of native Windows APIs as well, and as of R5.9, we are not aware of any leaks in our library. (Although we are aware of several leaks in Windows CE 6.0/7.0 that do affect our libraries as well, and which won't ever be fixed because Windows CE 6.0/7.0 already reached end-of-life.)