Conditions were not ideal, as there was cirrus in the sky. Yet the images (below) do show it's flashing behaviour, with a period of a few seconds (two maxima in each 10.7 second exposure). In the third image, Lacrosse 5 (05-016A) was captured as well.
Careful measurement of the images yielded the following flash-intervals:
Photo #1: 4.0s
Photo #2: 4.6 s
Photo #3: 4.9s