You understood correctly.
Interesting... If Fusion wants to hot-add memory, it means that it thinks the VM is powered on. (While the VM is powered off, we do a "cold add" which is much easier.) If it allows you to adjust the amount of memory, it thinks the VM is powered off or that memory hot-add is enabled. It then complains that memory hot-add isn't enabled when you try to adjust the memory size. Very strange!
What is the version of Windows you have installed in the VM?
The easiest way to attack this might be through a Support Information bundle: In VMware Fusion's menu bar, choose Help> Collect Support Information. That will create a file on your Mac's Desktop with all sorts of useful troubleshooting information. Attach that file to a reply (use the Browse... button below the editor here in the forums) and I'll take a look.
Cheers,
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Darius