@busybrian I was having issues with backslashes in any field, it was breaking the serialized data saved to the post_content and then it was unable to load the field at all. I wrote it up in another post and included some code that fixed it for me – I wrote the sample as a standalone class but am including it in my Validated Field plugin (however currently only in the beta version), which should also be forwards compatible if it is fixed in ACF.
Unfortunately if you have already performed the database upgrade for ACF5 then any fields containing backslashes will have already been corrupted…
http://support.advancedcustomfields.com/forums/topic/backslashes-in-field-attributes-breaks-acf5-import-save/
