It could be either way round. But in general, I don't think it's that difficult for a VetOp to reuse /nextmap (unless of course it is in the final few seconds of the mid round time)!
It is quite nice to troll people using this.
For example, say the next map is the same as previous map was due to that annoying glitch which leads everyone to /skip it.
It is quite fun to /nextmap PL-Warehouses (or another popular map) as people /skip the last time, this means that it is only the nextmap for a fraction of a second, and then it ends up with the nextmap being Evil. :) Happy days.