Incorrect Paid Through Date..anyone else?

I've been using Sitelink for about 4 years now. The past year has given me a lot of issues when it comes to Paid Through Dates. When a tenant is getting ready to vacate their unit, I let them pay by day and not by month. I have always gone to the pro-rate calculator and charged the amount shown for the particular days they will need the unit. Not always, but sometimes it shows the wrong paid through date on the customer's receipt. It is very frustrating to tell the customer that they paid the correct amount but the computer shows the wrong date. 

For instance.. a customer comes in and says that they will be moving out on August 5th (They are currently paid through July 31st) . I would go to the pro-rate calculator and select August 1st-5th. I would charge them the amount that it shows, and then it changes their paid through date to August 4th. I always use the same process but don't always get the same results. 

I have reached out to Tech support multiple times. Depending on which representative I speak to I am either told to charge an extra day (August 1st-6th) to get the paid through calculator to show the 5th or I am told that it is happening from a recent update. I've also been told that Sitelink has always worked this way, but that is not true because I get a different result using the same process. It is very annoying because I never know if the paid through date is going to work. I started adding the extra day and then I have upset customers who think that they have over-paid their rent when the pro-rated calculator decides to work correctly that day.

Is it just me, or does anyone else have this problem?