currency updating date shows wrong when set it monthly update

[Phoebe]

Hi,

I'm using currency_rate_update module. My requirement is the exchange rated should update monthly.
for example, I selected the service party is ECB, and in Company page, I chose 'Monthly' update.

In Jun2014, I want a new item with date '2014/06/01' and the rate should be the rate of the last working day(May 30)'s rate in May.

I applied this for several month. the rates always shows correct but the date field sometimes went wrong. It not always show the first day of each month, eg. just like the case above, it shows date equals to '2014/05/31'.

So I was wondering if there's a problem on the 'nextcall' field ?or I had some operating mistakes?

I found the definition for 'nextcall' is :
'nextcall' : time.strftime("%Y-%m-%d %H:%M:%S", (datetime.today() + timedelta(days=1)).timetuple() ), #tomorrow same time

I know this can be workable for daily/weekly/annually update cause the interval wouldn't change. but how it work for monthly updating? (days in months changes)How to get the correct 'nextcall' in monthly case?

I'm not sure if I understand this in a wrong way. please help explain or check. thank you in advance!