Incompatibility with hook-provided boxes and entity cache

[mkernel]

When using entity cache (https://www.drupal.org/project/entitycache) and hook-supplied boxes, one might get fatal errors when viewing a grid on the second request, as the classes are not prepared for the cached entity.

It might be that entity cache is not the problem - the setup the bug surfaced on has a lot of caching mechanisms. entitycache is an educated guess.