gistfile1.coffee

  someFunction: (date) ->
    startOfMonth = date.beginningOfMonth()
    endOfMonth   = date.endOfMonth()

    console.log startOfMonth.format('{MM}-{DD}-{YYYY}')
    console.log endOfMonth.format('{MM}-{DD}-{YYYY}')
    console.log '---'


# I call someFunction() with the SugarJS Date objects representing "12-09-2011" and "01-09-2012" and get this in the console:

# 12-31-2011
# 12-31-2011
# ---
# 01-31-2012
# 01-31-2012
# ---

# Why is `endOfMonth` clobbering `startOfMonth`?

# To get around this, I had to do:
   startOfMonth = Date.create(date.format('{MM}-{DD}-{YYYY}')).beginningOfMonth()
   endOfMonth   = Date.create(date.format('{MM}-{DD}-{YYYY}')).endOfMonth()

Maybe it is because you are calling it on the date object, and Sugar could be overwriting it?