Maintenance Plan Scheduling from Last Completion Date

I have a query regarding one of the Maintenance Plan with 3 months frequency.

Why is that the Planned date at row 3 is of 28th Aug when last completion was on 14 May 2015, as I was expecting it to be on 12 Aug as per 3 month frequency (90 days)?

Also it is required that the next date is exactly calculated from the last completion date, whats need to be done?

I have gone through different answers on scn but still needs assistance.

Thanks

Faisal