We converted a second home to a rental property on Sept 1 so I expected all expense categories to be pro-rated at ~0.33. Why do some categories use a different ratio?

Honestly, you're better off doing the prorating yourself rather than leaving it to Turbotax.

For example, management fees, advertising, and commissions, are all 100% deductible (no proration) as are repair/maintenance expenses paid during the rental period.

You can also deduct 100% of your utility bills for the Sept-Dec period. 

If there was no personal use AFTER it was converted to a rental, enter ZERO personal days.

Manually prorate annual expenses (such as insurance and real estate tax) so you only enter the amounts that applies to the rental period.

there are 2 ways to prorate some expenses. 1) general - number of days rented at fair rental divided by the total number of days the property is occupied prop reg 1.280A-3 2) tax court method upheld this method  (Bolton, 51 AFTR 2d 83-305 9th Cir. 1982) mortgage interest and taxes were allocated based on the number of days in the year. Expenses directly attributable to occupancy were allocated based on the number of days of occupancy