Why is the Alternate_Name_vod__c field populated with only the first letter of the Account's name on Offline devices, but shows the complete name Online?
This is working as designed. It is not suggested to place the Alternate_Name_vod__c field on the Page Layout, as it is used to hold the first letter that defines the initial steps of the indexing of the Account list. It sets which letter group the Account belongs to on the alpha-numeric sidebar.
CRM Help Documentation: Account Lists and Views