When a stock split happens, your shares change at a specific factor. Either you get more shares for a lower price or less shares for a higher price. Stock Events does not automatically adjust your shares, but it's easy to do it yourself. There are several ways.
If you use simple share mode
In case you use the simple share mode, just adjust your shares and average price according to the split.
If you use transactions mode
In case you use the transactions mode you can do it in two ways. You can either adjust all of your transactions according to the split or if there are too many transactions create a new transactions with a price of zero and the difference in shares at the day of the split.