I've never heard of this. YGTBSM!
17 years flying gliders, 12 years as an instructor, moving the spoliers at will, turns or no turns, no problems.

I've never read anything in any glider flying manual, FAA handbook, or aerodynamic study.
Better warn the airlines, no spoiler actuation during turns!

I love to do a flight review with some of those pilots and watch them when I use the spoliers.
BillT