“Sign in to download from the App Store” dialog does not allow paste OSX 10.8.5

I am using lastPass and have the appleID in there so I can copy and paste whenever needed.

Sometimes when I am told I have an upgrade I am asked to sign in to the app store.
Annoying but ok. So I have generated a quite safe password - why am I not able to paste that into the password field? Any setting I can change?
(I obscured the appleID in the picture below)
You can use Keyboard Maestro with a macro such as this which takes the current clipboard and inserts its contents by typing it rather than pasting, allowing the clipboard to be entered into fields where pasting is forbidden.

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Also, for what it's worth, OS X 10.10 Yosemite does let you paste into the aforementioned field and I believe so does 10.9 Mavericks.