I think I need an explanation of how the time works in JForex.
Im running a filter in onBar() on weekends as non valid trading days, like this:

    if (isValidDay(askBar.getTime(), Calendar.SATURDAY,Calendar.SUNDAY)) {
      ...
    }

    private boolean isValidDay(long lastTickTime, int ... days) throws JFException {
        GregorianCalendar gCal = new GregorianCalendar();
        gCal.setTimeInMillis(lastTickTime);
        gCal.setTimeZone(TimeZone.getTimeZone("GMT"));
        

        for (int day: days) {
            if (day == gCal.get(Calendar.DAY_OF_WEEK)) {
                print("Bad day! No trade!"+gCal.getTime());
                return false;
            }
        }
        return true;
    }

That seems to check out in backtesting. Yet heres what i got running real between sunday/monday night:

2012-05-07 00:00:00 Bad day! No trade!Sun May 06 02:00:00 CEST 2012

And before that:
2012-05-05 13:48:45 Order BUY 10000 EUR/USD @ MKT is sent at 2012-05-05 13:48:45.766 GMT by the strategy "Strategy8_4dfEURUSD": from the local computer

Where your server correctly responds with:
2012-05-05 13:48:35 System is currently unavailable. Please try later or contact Support Desk


So, from what i understand from the above code, the EA should not be able to get past the isValidDay() check, unless the date embedded in the askBar.getTime() is 1 day "off".

Could you verify/explain all this?

In the print method local time zone is used to format the time.
To be consistent GMT should be used to format time:

    public String toStr(Long time) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss") {

            {
                setTimeZone(TimeZone.getTimeZone("GMT"));
            }
        };
        return sdf.format(time);
    }

Thanks for the suggested method but the server is not running past the date line, so I see little explanation for a 26 hour gap.
I'd be suspecting a 2 hour gap given the server is on daylight savings time + GMT+1.

Additionally, theres no different enumeration of the days between Calendar and GregorianCalendar, that I've been able to find.

summer time trading hours are Sunday 21:00 - Friday 21:00 GMT.

Yes i realize that, only that GMT dont have summer time.
So when you query the server for what time it is, itll respond in true GMT times. Or at least such is the ways of Java and by the looks of it, your server too.

Anyway, thats not the issue at hand.
The thread was started due to this: 2012-05-07 00:00:00 Bad day! No trade!Sun May 06 02:00:00 CEST 2012
Which is a good day discrepancy in the date. Never mind the hour/timezone.

And that line came back from the server on a Monday, not a Sunday as the test is reporting.

It came from this bit of code that to my knowledge sets the time of the calendar to the tick time and tests if its a Saturday or a Sunday. Not a Monday.
And since its on a dayly chart in the onBar() event, i recon something needs to be explained.

Why do I get a "Sunday" from the system when the current weekday was a Monday?

if (isValidDay(askBar.getTime(), Calendar.SATURDAY,Calendar.SUNDAY)) {
      ...
    }
 
    private boolean isValidDay(long lastTickTime, int ... days) throws JFException {
        GregorianCalendar gCal = new GregorianCalendar();
        gCal.setTimeInMillis(lastTickTime);
        gCal.setTimeZone(TimeZone.getTimeZone("GMT"));
         
 
        for (int day: days) {
            if (day == gCal.get(Calendar.DAY_OF_WEEK)) {
                print("Bad day! No trade!"+gCal.getTime());
                return false;
            }
        }
        return true;
    }

Have you taken a look at the following wiki article?
https://www.dukascopy.com/wiki/#Customize_trading_hours/Use_Calendar_weekdays

Have you?

Put the programmer on the line, please. Hes got cargo pants and a t-shirt on. Cant miss him.
Its a bad idea to mock you customers and even more so when we somehow have wind up paying you to debug your own software.

First of all, we referenced the wiki example, because it is close to what you need and we have tested it to process the weekdays properly.
Second, work with dates is java.util functionality not JForex API, hence, if it does not work as you expect then it can't be JForex bug.
Third, when you encounter a problem, for more efficient assistance please provide:

• Full example strategy and launch scenario. The more concise the strategy, the better.
• Describe the behavior that you find to be wrong. Describe the behavior that you expect instead.

First of all, its not the wiki example thats wrong, but the day you return in JForex.
Second, your conclusion is wrong due to "First of all".
Third, you have received both code and explanation of what is expected of it.

JForex API works neither with days, nor dates. All date values get represented in milliseconds and the way you process them is what makes the difference. Thus you have to make sure you parse the dates properly.
Thus far we have received a code snippet which has nothing to do with JForex API. Hence, we have received neither a full example strategy nor a precise launch scenario, which makes it impossible to assist you on the matter.