I think you answered your own question. its a demo
Think about it for a moment. If you can test an EA right up to the last moment, then you can just copy those trades to your live account, and cheat.
Same thing for a trend indicator. If you test the indicator and back tester allows you to go to the last current tick, and the indicator says Trend is Up, then you can simply place a Buy order. Now you are using it to trade in a Real Environment.
By stopping demos being tested over the last few days it protects developers from those who want to abuse it... A good feature by MQL!