This is not unheard of, when a task is kicked off ... there's a grace period depending on the operation in which you're able to cancel. Once it goes beyond this value, you will not be able to cancel the task. Eventually it won't receive a response back and either it'll timeout or just error out.
The 2nd is a known issue as the time for committing a snapshot will vary depending on the size and the task itself actually times out trying to wait for the process to complete, even though it's still processing. To track an actual snapshot commit, you can follow these instructions listed in this VMware KB: http://kb.vmware.com/kb/1007566
For #1 just make sure if you have running VMs and it's part of a cluster, that you have DRS enabled else the VMs will just sit there, I've seen this happen in the past and the task will eventually timeout. Unfortunately there's not much you can do, best thing is to investigate on why it didn't go into maintenance mode in the specified interval, may want to look at the ESX logs or contact VMware Support if you continuously see this problem.
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William Lam
VMware vExpert 2009
VMware ESX/ESXi scripts and resources at:
Twitter: @lamw
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