Most likely, I would guess the mechanic left out a limit clip, or keeps reusing used ones that have lost their springiness, and/or left out one or more of the interlock pins. Refer to the R151 article in the tech section for an example of what happens and see if it matches your symptoms.

It's not hard to do it yourself, by the way...

-Bill
'87 4Runner w/ '96 5VZ-FE, 'Red Chili II'
'97 Taco XtraCab 3RZ-FE, 'BlackBean'
TLCA # 13257, Rising Sun 4x4 Club Land Use Coordinator
"He who stops being better stops being good." -Oliver Cromwell