Using Gravityforms v126.96.36.199.1 and WP 3.3 with Headway 2.0.13.
Based on the contents in a database I'd like to pre-populate - using gform_pre_render() - the state of a months worth of checkboxes (i.e. the checkbox is selected/checked if there is content saved for that column in the database table).
The data gets saved correctly (so I believe my gform_after_submission() function does "the right thing").
It's upon subsequently reading the data that the checkmark for the previously selected/checked checkbox will "jump" one additional space (day) out in time for every 10th day. Meaning, pre-save, if I checked the checkbox for day 25, it will be rendered as checked on the 27th day when I go back to the form after saving. If I'd checked day 10 pre save, it will now render as day 11, etc.
When checking the database, the correct column - i.e. the column for day 25 - _is_ set in the table.
I've got the code I use pasted here: http://pastebin.com/xmcmBWD7
Also, I've got screen shots of the pre and post save form at the following locations: