The amount on line 43700 seems to be incorrect. Why is this?

When you split your pension income with your partner, you must also split the tax withheld that is associated with that pension income.

You can see how line 43700 is calculated for both the Pensioner and the Transferee in Step 5 of form T1032. This calculation overrides the regular calculation for line 43700. Find the T1032 in the Summary section.