Never noticed this, because I always use the custom filter option, not the basic. But I had a user come to me asking why his app wasn't updating his filter properly.
He configured the filter tool thusly (dummy data):
And here is the what the action tool looks like when you connect it to the filter tool:
So he simply highlighted the "Bob" line and picked to update "Bob".
However, since he used a basic filter, and not a custom one, this is how he should've configured the action tool:
I realize that "well, it's spelled out for you - there's an expression section & a simple section in the action tool". But for beginners or even non-beginners, it might not be obvious.
It would be nice if when you connect the action too, it only displayed the appropriate option (either custom or simple, but not both).