Hi Daniel.
This is a trait of fast Newtonians. There are several things you can do to reduce the effects of the square star syndrome.
Using a special type of curve when stretching is one keeping the mid to highlights part of the curve flat. The other is separate the stars and process them separately which is becoming a bit of a trend with the development of star removal tools like Straton, Starnet++ and StarXterminator.
Unfortunately fast reflectors all suffer with it - comes across as a flaw, which it is not. Its just a characteristic
Cheers
Peter