A wise Forum member (FP) told me a little trick "way back" that keeps these caps in place. Otherwise, they will come off randomly without warning whenever wipers are used.

Get a roll of smooth electrical tape. Cut a piece off that is no more than 1/2" long. Cut a piece that is no wider than the recessed flange section of the cap. Place that piece along the recessed flange section that inserts into the wiper arm (doesn't have to go all the way around the cap). This will create enough of a "press fit" to keep the wiper arm cap secured. I've used this technique on my Crossfire and the caps have never come loose.