Thanks guys - I did figure it out with help from Jeff's links. I want to be clear that I was mistaken and this is a P3D issue only... it doesn't happen in FSX.
Just for other P3Ders who may run into this problem, here's what I found...
The problem was related to one of the AI shipping packages that I had installed from the Return to Misty Moorings site. The boats shooting wakes to the stars were all using the effects file fx_wake_coastguard.fx for their wake effect. That file has some entries that my other *_wake.fx files did not, all located under the sections [ParticleAttributes.x] where x = 0, 1, and 2 (so there were three sets of the following lines, all of which had to be changed). These were the lines in question:
TempK=109.00
TempRate=0.01
I saw a comment somewhere where Holger Sandmann said that these lines could cause the wake to act like steam, not water, so that the wakes would rise. So I commented them out in all three places...
//TempK=109.00
//TempRate=0.01
And it all works perfectly!
Thanks to all of the RTMM team for the best FSX addon... it is a joy to explore and use.
Scott