for in syntax won't iterate through every property of a arguments object in a function context.

This bug affects the jquery.extend function.

Because the implementation trys to iterate through every property of an object using this approach.

Implementation: https://github.com/jquery/jquery/blob/master/src/core.js#L333

My currently work around for this is to create a copy of the arguments object before passing it to the jquery.extend function.

See a demo of the bug:

http://jsbin.com/akanov/7

Tested Chrome and it works as expected.