In QuantConnect, historical data is adjusted by default. This means the historical values are changed to account for share splits and dividend payments. Historical prices can look a little bit strange if you don't understand why it was done: e.g. instead of $10.23 the price might read $1.21216.
You can control the Data Normalization Mode for each asset individually. This is done with the: security.SetDataNormalizationMode() method. The accepted values are: Raw, Adjusted, SplitAdjusted and TotalReturn.
ibm = self.AddEquity("IBM", Resolution.Minute) ibm.SetDataNormalizationMode(DataNormalizationMode.Adjusted) //Default