See, when you deposit in post office time deposit (POTD) it's principal amount would be allowed as Deduction u/s 80C if maturity period is above 5 years.
Interest amount would be fully Taxable but if received by Senior Citizen it is exempt u/s 80TTB Upto Rs. 50,000.
TDS:
Post office would deduct TDS on interest paid. y it. In case of Senior Citizen if there is amount of interest payable exceeding the above said limit of Rs. 50,000 then TDS under Section 194-A @ 10%. Although you have to show income under Other sources in any case and then claim the TDS from your Gross tax liability.
Income from Post Office Term Deposit is treated as Fixed Deposit. If it is for 5 years term then it is exempt u/s80c. Though the interest amount at the time of maturity is calculated as income in the hands of the depositor.
See, As far as CS study material as I earlier said you once that there might be mistakes crept in that that has been happened so many time (as I'm a CA finalist so in our syllabus too we have seen many mistakes).
As far as Cumulation is concerned in POTD interest it is generally cumulated quarterly but still Interest would have to been yearly and has to be offered for tax.
Suggestion:
Do remember that there is allowed Deduction u/s 80TTB ONLY FOR SENIOR CITIZEN Upto Rs 50,000 of interest.