I'm not entirely sure about Lacerte, but the 'default' for ProSeries is to NOT use the MACRS tables.  The way it does it using the mathematical way, things get funky when the business percentage varies.

You generally aren't supposed to switch in mid-Recovery period, but because it was only one prior year I don't see a problem with changing if you want to.  Look for something that says to use the MACRS "tables" (in ProSeries it is WAY down near the bottom).

Otherwise, it hypothetically may be correct.  I say "hypothetically" because there is some question if the order of operations is correct, but at any rate, several major software programs treat it this way when they use the mathematical method without the "tables".