The array of values from a list field type are serialized twice before being stored to the database.
Specifically it stores this:
s:48:"a:1:{i:0;a:2:{s:1:"a";s:1:"1";s:1:"b";s:1:"2";}}";
rather than this:
a:1:{i:0;a:2:{s:1:"a";s:1:"1";s:1:"b";s:1:"2";}}
Are you having trouble retrieving the values you need, or some other trouble?
I've pinged the developers to see if they can add anything here.
I also found this related information:
http://www.gravityhelp.com/forums/topic/list-field-help#post-39885
I have figured out how to retrieve the data, but I thought I would bring to your attention that list data is being twice serialized. This is a bug.
If it helps, I am retrieving the list data from the user metadata tables after using the User Registration add on.
I am not able to replicate this issue on my test site. The list field is stored correctly (only serialized once). I believe I have seen this before and it ended up being a conflict with another plugin. You may want to go through the Plugin and Theme conflict process to find out why this is happening. (http://www.gravityhelp.com/documentation/page/Testing_for_a_Theme/Plugin_Conflict)
