Great Western Coffee Shop

I have been playing with the FCC season ticket calculator:

http://tickets.firstcapitalconnect.co.uk/cc/en/JourneyPlanning/SeasonMixingDeck

Selecting a start date of 30 November and selecting 3 Months' validity puts in an end date of 28 February. Yet the search results come up with an end date of 27 February.
Amending the end date to 1 March still comes up as 3 Months' validity.

Just a bit confused to how this is worked out. Take another example, a 1 month season ticket commencing on 29 January would be valid until 28 February (using -1 on the date and +1 on the month). A total of 31 days.

So a ticket starting on the 31 January should last until 2 March to be consistent?

Just to add, obviously it is only with February that I encounter this. Selecting a season ticket starting for 1 month on say, the 31st of another month, will end on the 30th of the next as it has at least that number of days.

My monthly season tickets used to be valid for the number of days in the month that the ticket started in.

Odd period were issued for x months + x days where the number of days in a month is calculated like multiple consecutive monthly tickets.