Mail.app keyboard shortcut conflict

Hello,

I'm using Things to manage tasks on my iMac (OS X El Capitan, up-to-date).

Things has a keyboard-shortcut-based quick entry feature to add tasks with autofill from everywhere on the Mac.

For example, from Mail.app you can press ⌘⌥⎵to create a new task with a link to the e-mail you are on.

The problem: from mail.app, pressing ⌘⌥⎵opens the new autofilled task windows and the Mail.app Activity window, even if the shortcut for Activity is ⌘⌥0.

I tried to change the keyboard shortcut in Things, but the problem is still there, no matter the shortcut.

I went into Preferences > Keyboard > Shortcut and there are no reported conflicts.

So I tried to to manually add (overwrite) the shortcut ⌘⌥0 for Activity window in Mail.app — no way.

Anyone can help me?

Thanks.

Alessandro.