Incremental markername (e.g. letters) throws error in IE6 & 7

I've ran across this issue on my local test site and on the following demonstration site (given on the module homepage):
http://gmap.chicagotech.org/map/macro

Basically, if you set that marker to be 'letters' or 'numbers', it will throw an error in IE6 & 7

Steps to recreate:
Go to demonstration page (http://gmap.chicagotech.org/map/macro) in IE6 or IE7
In the dropdown for 'Marker:' choose 'letters' or 'numbers'
Click anywhere on the map to place a marker.
When you click, it will throw an ambiguous error pointing to line 13 in google's code

Oddly enough, the 'week ' markername seems to work.

Let me know if you need any more information