Question about DTI and joint debt

[Georgina Prager]

I have a DTI question. I co-own two properties with joint mortgages and we need to refinance to separate the properties and mortgages. The plan was for me to refinance the property I'm keeping, then the other owner will refinance after the 3 day period.

My DTI will be very low - maybe 15%. The other owner will be at about 33% DTI after the refinancing

Days before the planned closing the underwriter recalculated my DTI using only my salary and the full payment for both properties. The reason they gave is that there is risk during that 3 day period. I get that but the 2nd property will still be a joint liability at that point so they should also be using the co-owner's income in the calculation.

How can I find out more about the rules for calculating DTI when the debt is a joint loan?