The thing about incoming fats is that they won't be used for energy for a few hours anyway, so your body will be running off of it's available energy sources. The body takes at least a few hours to process the ingested fat before it is available for energy right away. The main problem with ingesting fats post work out is that it will slow down digestion and absorption of that pwo meal, and thus the amino acids and the carbs/glucose will take longer to reach the muscles needing repair.
I don't know/remember if breaking down the ingested fat is faster or slower than breaking down adipose tissue, however, if you just exercised there are FFA's around, waiting to be oxidized anyway, so you will be burning stored fat right after your workout anyway, in combination with some of the broken down carbs you just ate PWO, though most of it, ideally is going toward repair and refueling.
If I'M wrong or provided incomplete info, someone else can bust in on this and add/correct what I just said.