[Plugin: Ajax Event Calendar] Incompatibility with Jigoshop plugin (Javascript error)

I am using the Jigoshop plugin together with Ajax Event Calendar.

I can add new events, but I cannot edit an existing event in the admin section. The edit form won’t open (it says “loading the …” but nothing appears).

Firebug says that there is a javascript error: “this.getFullYear(); is not a function”. The function with that call is isLeapYear() in jigoshop_backend.js at line 101. This function is added to the Date prototype by Jigoshop.

The error happens when the JQuery call to content.load() in jquery_init_admincalendar at line 296 happens (this is in the javascript of ajax event calendar).

The top of the call stack looks as follows (not very useful).

(?)()jigosh...ver=1.0 (line 101)

g()wp-admin/load-scripts.php?c=1&load=jquery,utils&ver=fb..61 (line 18)
a = "event[start][isLeapYear]"
b = function()

f()wp-admin/load-scripts.php?c=1&load=jquery,utils&ver=fb..61 (line 16)
a = "event[start][isLeapYear]"
b = function()
c = undefined
d = function()

f()wp-admin/load-scripts.php?c=1&load=jquery,utils&ver=fb..61 (line 16)
a = "event[start]"
b = Date {Fri Oct 14 2011 00:00:00 GMT+0200 (Romance Daylight Time)}
c = undefined
d = function()

f()wp-admin/load-scripts.php?c=1&load=jquery,utils&ver=fb..61 (line 16)
a = "event"
b = Object { id="2", title="Test title", start=Date, more...}
c = undefined
d = function()

The “this” when the function is called is the Window object. Which explains why getFullYear() is not defined. The question is: how come the isLeapYear() function is called on the Window object (and why it is defined on the Window object)?

This error appears to be in an infinite loop or something, since it appears over and over indefinitely (about 10 times per second, after a few seconds, firebug counts hundreds of errors in the console).

Any help would be greatly appreciated.

https://www.ads-software.com/extend/plugins/ajax-event-calendar/