Webform (Contact Create API) doesn't set Communication Style
If Communication Style is set to Formal -> is_default on:

civicrm/admin/options/communication_style?reset=1


Then that's what shows in the Contact record (see below); Are you saying that webform_civicrm removes this default for existing contacts; or that new contacts have their is_default set wrong? 



Added: I've confirmed that creating a New Contact with the API leaves the Communication Style 'blank'. However one would expect it should be setting it to the default value that is specified in the Administer settings.

So it's an API issue - we could fix this in webform_civicrm - by explicitly passing on a value for Parameter Communication Style - but I think it should be fixed in CiviCRM Core itself.