Tax form error question

I am doing my taxes and usually just print out forms and do it by hand and believe i caught an error. im in california (community property state) and am filing MFS. on schedule A line 5e i am trying to work through the State and local tax deduction worksheet (page 7 instructions). and i am getting two separate numbers when i do MFS or MFJ. i think the issue is line 1 where its asking to just put 40,000, rather than 20,000 for MFS. even though line 10 is asking you to divide line 9 by 2 if you are MFS, its too late in the math, as they are using the split income to compare with the joint cap of 40k

I am getting like an extra 7k of a deduction because of this.

am i messing up on something or are they