Please measure what's leaking/kept around and through which references. Objects can be kept in memory in .NET for longer than one anticipates through event handlers and references from objects which are cached. THough this also should be present on older .net versions so I have no idea what might cause the memory leaks.
Also, 'memory leak' is too vague: without a memory profiler you can't say it's our code which leaks... or that there is a memory leak at all (it might be the GC kicks in later than on earlier .net versions making it clean up memory slower than on earlier versions so code which quickly consumes memory in a loop might hit a memory limit now while it wouldn't in earlier .net versions.
