By the way, are you sure that MT4 really uses incomplete candles for its indicators? This would be a severe bug in my opinion.

For instance, the ATR is a very often used indicator. It is based on the high and low of a candle. When prices follow a normal distribution, the high-low distance is proportional to the square root of the candle width. Incomplete candles have thus a smaller vertical size than full candles. They would cause false trade signals or wrong stop levels when used for an ATR. At the begin of the candle, the high-low distance would even be zero.

Many other indicators would also be wrong when incomplete candles are used.