Some people have taken their foreign plated vehicles out of Mexico but for whatever reason did not cancel their temporary import permit at the border.
People should always cancel their TIP but many times it is not feasible to make that long trek back to the border and have to cross over and cross back.
Benefits of canceling are receiving your deposit back (if you cancel permit before expiration and / or timely done extensions), being able to temporarily import another foreign plated vehicle into Mexico and not having any future worry or hassle due to the Mexican government thinking your car is still in Mexico.
The Mexican consulates in the US have special days where they will be canceling permits at their US based consulates in the following cities and dates for the rest of 2015:
Denver Thursday and Friday October 8 and 9 2015
Houston Wednesday, Thursday, and Friday October 14, 15 and 16, 2015
Dallas Friday, Saturday and Sunday October 23, 24 and 25, 2015
Sacramento Tuesday and Wednesday November 3 and 4, 2015
Los Angeles Thursday and Friday October 29 and 30, 2015
Phoenix Thursday and Friday November 12 and 13, 2015
Chicago Thursday, Friday and Saturday December 3, 4 and 5, 2015