Is the 50% function for the T5, box 13 working? In the income summary and T1 General full amounts are indicated in both my spouse's and my returns. Should this be so?

You only need to enter the T5 slip on "one" spouse's tax return and specify the 50% split. If you enter them on both returns, it will result in each of you claiming 100%. 

If you have mistakenly entered the slip on both returns, you'll need to go to the T5 Slip Summary page and delete the entry from one spouse's return.