Is this something that has happened just once or multiple times ? Did you use a correction factor prior to starting on the pump, and if so, is your pump correction factor similar to pre-pump ? Was your activity level more than usual ? If you can eliminate other factors, and based on your pre-pump corrections, you should be able to judge if your pump factor needs adjusting.
When I do a correction, I don't rely just on my current BG and pump calculation. I think about other factors and may adjust the pump calculation as necessary. My goal is to get the pump to calculate an approximate correction amount, and then I may increase or decrease the result.
This is more of an art than science, and each person is different.
MEGAMINX i do exactly the same you do...i use my brain to decide if i should do what the pump says or not...sometimes i do & sometimes i don't.
I wouldn't make changes based on one experience, but keep careful watch and see if this ISF is bringing you too low. If it's happened before you might want to reduce it a bit to be safe and then see how it works. I always make changes based on a pattern, not a single occurance.