As ender` writes, it is a general UI problem that happens to only manifest with Windows NT 4 guests, but could potentially affect other guests as well: Any guest with VMware Tools to support shutting down the guest OS, but without the capacity to actually power off the VM, or possibly other scenarios where some component hangs during shutdown.
We still have an internal bug opened to track the issue, but as WoodyZ suggests, we do have to prioritize according to customer impact (and hence age and prevalence of the known affected guest OSes).
Thanks,
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Darius