CAPTIVATE-FR2676: BIC.B and BIS.B to set and clear a port pin, appear to vary in clock cycles

I am working with the MSP430FR2676 Micro, on the Captivate Evaluation kit (using the associated debug interface provided by TI for this board)

I am experiencing a strange situation, where repeated set and clear of a port pin, varies between 5 and 6 clocks

I suspected JTAG clock stealing, but when I disconnect the debugger and run the board stand-alone, it does the same thing.

The variance follows this pattern - 5 6 6 6 5 6 6 6 5 and so on

Here is the code

In the scope capture below, CH2 (green) is MCLK

(Note how the first low pulse is 5 clocks, where the second low pulse is 6 clocks)