When you use the Notepad++ Plugin Manager and it needs a restart in order to apply the changes clicking yes in the restart dialog will silently fail, the dialog dissappears and Notepad++ doesn't restart this causes this dialog to appear again and again each time you start Notepad++ and I think it also doesn't install the update because of this.
I'm not sure whats causing it whether it might be saving the downloaded plugins in the wrong location or maybe because the launcher causes it to fail to restart itself for some reason.
Please fix this, it's quite annoying not behing able to use the manager and/or update plugins with it.
EDIT: Topic in Notepad++'s forums: Plugin Manager issues under Windows 7