Var textsizeCookieExpires "365" is set as a string causes an error with jquery.cookie.js

I'm getting this error in Firebug console when I try to change the text size 'TypeError: options.expires.toUTCString is not a function'

It's referring to the following line in this file jquery_update/replace/ui/external/jquery.cookie.js:

#78 options.expires ? '; expires=' + options.expires.toUTCString() : '', // use expires attribute, max-age is not supported by IE

The variable textsizeCookieExpires "365" is set as a string in textsize.module, something that was a number in previous version.

Changing the textsizeCookieExpires to a number resolves the issue.

Can anyone tell me if this is an error in the code? Or is there a reason why textsizeCookieExpires is set as a string?