I had subarus with frameless windows and to my knowledge they never did automatically go down slightly when opening. If you feel like it's sticking, you can condition the rubber seals with something like shin-etsu 08798-9013 silicone grease (best), or multi-purpose Sil-glyde (good enough)
Sil-Glyde Silicone Lubricant
Sil-Glyde Silicone LubricantDescription Sil-Glyde Lubricating Compound A longer-lasting, high film strength protective lubricant for all surfaces, including: rubber, metal, wood, glass, and plastic. Won't melt, freeze, gum, or run off. Performs from -20 deg F to +400 deg F. Grease consistency...