Interest liability on tds on salary

Dear all

Please let me know one thing that if during the fy 2013-14 we are assuming that we should not deduct tds because we will make the investment but in the month of Dec,13 we realise we can't do the same. 
 

In such case accountant will deduct the the entire tds till the period of Dec,13 in the same month. or

you can say the tds deducted on salary every month ,presume, was lower than that should have been deducted.

Then in both the supra cases, Is there any interest liability arises, specifically, in the case of salary?

Regards

Pradeep