Why doesn't OnChartEvent continue working?

I wrote an indicator that draws symbols on the chart once I draw a trendline. I wrote in the OnChartEvent function to run the code every time I drag the trendline. It works finitely many times, and then all of a sudden the symbols on the chart are frozen, no matter how many times I change the trendline. The only way to fix it is to remove the indicator and reattach it to the chart. Does anyone have these problems?