Error modifying graph, because of automatically added extra symbol definitions

[kschlebusch]

Within SAS EG 6.1 the graph gui creates a graph with 20 symbol definitions but from symbol14 it only repeats "symbol1".

When trying to modify this task, SAS encounters an error and claims "The value entered, 21, is invalid.
Please enter an integer value greater than or equal to 1
and less than or equal to 20.
Parameter name: Index for columns to plot
Actual value was 21."

By manually removing the 6 "symbol1" declarations, the code worked fine. How is it possible those got into the code?