@Diane298, it can be confusing, and you are not alone in having something like this happen.
One thing that will help is that the "minimum price" is just the smallest amount that will be set for a single nights rate. It does not take into account any other discounts or special offers you apply.
For example, if you set your minimum price to be $100, then the smallest amount for one night will be $100. However, if you have a monthly discount of 30%, then a person booking for a month will pay less... in this case $70/night, if the whole month were set to $100.
I know you complain that it reduced your price below your "minimum pricing", but think about what would happen if it did NOT do that.
Imagine the alternative: A guest sees that you offer 30% off if you book an entire month. He sees your nightly rate is $100. Cool! they book 30 days... and the price is $3,000 because the system is not allowed to reduce the price below the "minimum pricing". Essentially, your discounts become meaningless, and the guest would feel that they were being lied to. And, in fact, under this system, they are being lied to.
So yes, it can be confusing. But that doesn't mean that the alternative would be any less confusing.