Prior to Drupal 7.7 we had an inconsistent behavior when initializing the field 'translatable' property all around core, seefor details. The solution outlined there has been committed without the related update, since it was not possible to provide test coverage for it. We still need an update ensuring that also D7 sites created before D7.7 get a consistent behavior.
Quoting from the parent issue summary:
The tricky part is how to deal with existing sites: since translatability can be changed in any moment, originally we agreed that only sites that never dealt with field languages should get a fix, this means sites with no translation handler enabled and no field value in the database with a language assigned. This could be checked in a field-storage-safe fashion through EntityFieldQuery. However since update functions cannot rely on entity information () and they cannot cause hooks to be invoked, there is no way to implement a perfectly working update function.
We decided to fall back to an update function only checking if fields have any language associated, in which case no change to field's translatability should be performed.
The update code is ready but we need test coverage for it, which is not possible to provide at the moment, since we have no support for testing minor updates.is postponed to .