There is a bug that triggers when you add a funding round. It takes your equity percentage down to zero, regardless of the amount raised or pre-money valuation.
How so? I agree that as soon as you add a round of funding, the math gets wonky.
For example, I'm trying to model what a ~5% ownership looks like, and as soon as I add a round of funding that creates 10% dilution with no liquidation preferences, the site says the final ownership percentage is zero. It doesn't even matter what the exit is for at that point, without liquidation preferences, the ownership should still be ~4.6%.