One Shot vs Continuous Fill
You can use the Fill options in different ways:
One shot
When you click one of the Fill buttons, it is highlighted and enabled during the next automation pass. Afterwards, the option is disabled again.
Continuous fill
If you click a Fill button a second time, a lock symbol is displayed on the highlighted button, indicating that you are in continuous fill mode and that the operation can be repeated as many times as you want. Click the button a third time to disable the corresponding Fill option.