Hanging on to memory begining with Elemental.

My observations:

If my memory is correct, the issue has persisted beginning with Elemental: Magic at War. I can say for certain it was around with the Fallen Enchantress Beta.

For about thirty seconds _after_ the GUI closes, the game hangs on to 90-100% of it's allocated memory.

For about one to two minuets (rarely longer) _after_ the GUI closes, it will hang on to about 40% of it's allocated memory.

After playing for about a hour, the game will not well and truly close for about thirty seconds to two minuets after I press the 'exit' button unless I force the OS to close it with task manage or logging off. In which case the executable will instantly close down. I know this because if the engine doesn't exactly leak memory, it does hold on to resources for extended periods of time to the point of clutter. To the point I save time by exiting and restarting the game every one to two hours.

My question:

Why does the game take so long to release it's memory? The C/C++/C++11 standard container objects are not _that_ slow.