Mine does the same thing. I never thought of it as abnormal in any way -- whether through wear or by poor design. When it happens, I just move the shifter back to neutral and let off the clutch pedal. It usually goes right into gear when I try it again.

As for the fluid, I actually tried a few others. Valvoline Synthetic Gear Lube was terrible - the car shifted like that old Ford Econoline three-on-the-tree that I used to run deliveries with in my college days. When I switched to Redline MTL (70w80) and then to Redline MT-90 (75w90), the shift quality improved back to stock and then actually very slightly better, respectively. None of these fluid changes had any effect on the "parked into reverse" phenomenon that you originally inquired about.

--
Jim Rothe, '99 S70 T5M,
http://www.jimrothe.com/volvo/index.html