Better than storing dirty! LOL. Seriously, its the normal. If you want leave a little Star-San in the keg. Than when your ready to use, you can just shake and dump.
The longer one leaves a kicked keg before cleaning the more work will likely be required.
I do pour a splash of Star San mix into a freshly cleaned keg before pressurizing and checking for leaks (this is the least stressful time to fix a leaking poppet!)
But when I go to fill said keg, it gets fully Star San purged immediately before filing...