Medved Trader caches the data that it gets throughout the day and for charts, so when a split occurs, you need to tell it to adjust. Here is how to do it
Click on the portfolio editor button on top top of the portfolio window or Edit Portfolios tile on the dashboard.
On the portfolio Editor, click on the symbol that split, then in the window that comes up specify the split ratio and check all the boxes. Specify the Split date, though should already be defaulted.
If you have more than one symbol that split, repeat the same thing for the other symbol.