LH surge in pink dye but not digital

Okay so I had a solid smiley and blazing positive on a pink dye opk. First time using digital. I started testing early and always got the empty circle. Then I tested and got a solid smiley (never got the flashing smiley) and a pink dye with definite positive. Next day I tested again because I wanted to see how long my surge was. Only the digital was back to the empty circle but the pink dye was still clearly positive. I had this happen three separate times. My opk pink dye is now back to the test line being faint. So pink dye had my surge for about 36 hours but why did the digital only last about 12?