This problem is many a times, noticed by me and my x-clanmetes. Today, I got a chance to say it.
While donating in clans which are level 5 or more, some troops are not leveled up! This generally happens with dark troops, but sometimes also with non-dark troops. I myself many times see players having level 1 troops in their cc when they are in level 5+ clan (the players were permanent to the clans and had not taken donations from any other clan).
Today, this bug was faced by me. The clan I am in, is level 9. I and my clan leader, both were online. My clan leader had pekka level 3 and balloon level 6. I requested for pekka and balloon, as I needed to attack in war. I recieved pekka level 4, that's fine, but I recieved balloon level 6!!!!
That's a bug. Supercell, please fix it, or one day it will affect my attack!