Salary for pro rata term time

[MrsB247]

I recently started a new job (April) as an LSA within a college, full time term time. I picked up £374 less than expected - this showed up as a deduction.
I queried with HR who said it's because I have started part way through an academic year, and I will have the correct full amount in September.
Is anyone up on HR/Payroll who can advise if this is correct?
All my colleagues have said this never happened to them?
Was expecting a full time salary based on my pro rat term time.

Does the salary include holiday pay, because often TTO can't actually book any holidays - if it does, then it might be down to that (you won't accrue the full year's worth of holidays).

What does it give as the reason for the deduction on the payslip?