Error when changing string value in en.yml

[haydenholligan]

Whenever I change a value in en.yml and reload the page, I get the following error. To fix the problem, I have to reset the server with the I18N_BACKEND flag off, load the page, and reset the server with the flag back on.

Stack trace:

Line 48 is when the Backend class calls super. Haven't yet investigated further than this.