using statement on IDisposable object - delay of calling Dispose method

As describe this article, about usage of using on IDisposable objects, it says one interesting words:

...using block, the Dispose method is automatically called sometime after the block ends. (It may not be immediate; it depends on the CLR.)

Interesting here is "It may not be immediate; it depends on the CLR". Can anyone provide more details on this? Because we have some strange situations where it seems that on code using(new MyDisposable()) {...}, after end of block } it does NOT immediately calls Dispose method on MyDisposable instance, but some time later.

UPDATE: Conclusion for me, it seems to me that i have problem elsewhere. I think that Dispose method can be called some time later after using block ends. But when it is not like that, than i must find problem somewhere else in my code. Thanks for responses!