hi there mate
noticed this myself from time to time and found that lines like 40+ and scierra xda ( now discontinued ) overcome this slightly , probably due to the fact the coating on the lines were more plastic like rather than a matte feel to them
all be it i have sometimes had this again with the 40+ line i use now and have found also that when retrieving line the line seems to stick to the rod also between the rings near the tip of the rod and would say that it is caused by algie on the water surface or anything else that may be floating on the waters surface as i could also feel it on my fingers on a day at bangour fishery

the line would slow down during a shoot and left me to believe it was the above cause as once the rod was left for a while on the bank it became fine again
my opinion would be to buy a more slick type of coated line like most distance casting lines like the 40+