If he forgot to make sure all consecutive barracks levels got that string... (and he was already past lucky-level-L in test-city...) .
Nothing as rewarding as squashing a bug generated by your own code:
1) It works!
2) It's always good to see your intellect prevails (even if it is over your own intellect itself)
3) While de-facto it is very much like trial/error correction of your own Math test; it is not quite as depressing somehow.
Spoiler Alert, click show to read:
Bookmarks