This question/problem came up in the Backdrop CMS issue queue. The problem arose when someone was porting a D7 module that stored configurations at the root level of the field instance definition. Those custom configurations did not get saved. Backdrop doesn't allow custom configurations at the root level of the instance - it restricts that level to specific, pre-defined keys, and ignores everything else.
The solution is to modify the custom module to store its custom configurations inside the settings
element of the instance array. Then it will get saved. For example, you could store your settings like so:
$instance['settings']['my_module'] = array('setting_1' => 'asdf', 'settings_2' => 'zxcv');
Recent comments
The module is a port from the Drupal module of the same name and the name is not normally changed. Looking at the Drupal module there is this issue: https://www.drupal.org/project/...
Entity reference default value cant be saved
The maintainer should change the name of the module and not give wrong impressions.
Entity reference default value cant be saved
The README says: This module enables to use tokens for field default values in simple field types like text or select list. That's a convenient way to pre-populate fields when...
Entity reference default value cant be saved
The problem seems to be related with Field Default Token module. The coder put alot of comments in field_default_token_form_field_ui_field_edit_form_alter function saying the validation...
Entity reference default value cant be saved
Right. That's a bit more involved; I don't have time to reproduce that at the moment; perhaps someone else will. I'm sure it will be possible to port the module to Backdrop. You could put...
Entity reference default value cant be saved