Currently when processing event registrations and updating account information, there is an indication when the original account doesn't have information listed for a particular field (<blank>). This allows you to either choose if you want to keep the field blank or update it with the new information from the event registration. The problem is, this doesn't apply when a registrant leaves a field blank on the registration but already has something entered in their account.

The most common occurrence I have noticed related to this is when a parent doesn't enter their email address in the event registration but already has an email address listed for their account. When I process one of these registrations, the system overwrites their email address and leaves it blank, removing the user's email address. There is no indication that this is going to happen and the only way to correct it is to go into the individual registration and manually enter the address.