This is a major drawback of traditional reference counting garbage collection. The property of a garbage collector describing this behavior is an incomplete collector. Other collectors largely fall into a category called tracing garbage collectors, which include traditional mark-sweep, semi-space/compacting, and generational hybrids, and don't suffer from these drawbacks (but face several others).
All of the JVM and CLI implementations I'm aware of use complete collectors, which means they don't suffer from the specific problem you are asking about here. To my knowledge, of those Jikes RVM is the only one supplying a reference counting collector (one of its many).
Another interesting thing to note is there are solutions to the completeness problem in reference counting garbage collection, and the resulting collectors demonstrate some interesting performance properties that are tough to get out of tracing collectors. Unfortunately, the highest performing reference-counting garbage collection algorithms and most completeness modifications rely on compiler assistance, so bringing them to C++'s shared_ptr<T> are difficult/not happening. Instead, we have weak_ptr<T> and documented rules (sorry about the sub-optimal link - apparently the documentation eludes me) about simply avoiding the problems. This isn't the first time (another mediocre link) we've seen this approach, and the hope is the extra work to prevent memory problems is less than the amount of work required to maintain code that doesn't use shared_ptr<T>, etc.
The mediocre links are because much of my reference material is scattered in notes from last semester's memory management class.
