PTB leaves a stub behind on host PC?

I was cleaning out the registry on one of my computers, and noticed to my surprise that PTB showed up in it. It's under the key:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\UnreadMail\userid@isp.com
(the email address above isn't real, of course)

Where the string named Application has the value:
"G:\Apps\PortableThunderbird\App\thunderbird\thunderbird.exe" -profile "G:\Apps\PortableThunderbird\Data\profile" -mail

Luckily I haven't used PTB on any public computers yet, but the fact that my email address is left behind on a host PC worries me. Is there any way to fix this problem?

Thanks.

Edit: While typing up this post, I figured to look at another one of my computers, too. Same thing (well, the drive letter is different). It's PTB 1.5.0.2 on WinXP Pro SP2 on both computers, if that matters.