[SalesForce] Transfer Account Owner, Keep Account Team

Using a trigger to maintain the prior value is always an option.

Have you looked at enabling Team Selling?

http://login.salesforce.com/help/doc/en/customize_teamselling.htm

I believe that's the only dependency to having the 'Keep Sales Team' option appear when you're transferring an account to a new owner which would solve your problem as long as the user doing the reassignment remembers to check the box.

There is a checkbox that allows you to keep the account team when changing the owner as described here:

You might be remembering something similar to the idea out there requesting this be checked by default so account teams aren't accidentally lost when not checked:

When assigning an account, it is not possible to lock the account team: there is no control on the checkbox "keep account team", and no API access around assignments. (note: maybe one can create an Apex trigger for it, but it wouldn't change the UI of the assignment page)

Edit: Another idea here also states it is not possible to keep the account teams via API as you thought:

Allow Keep Account Teams and Keep Sales Team when changing owner via API. Essentially, if we change the owner via the API we don't have the ability to have the Keep Account Teams and Keep Sales Teams checkboxes checked like you would if you manually changed the owner via the UI.

Edit 2: After testing I also confirmed that the account team is kept when the account owner changes, in the workbench, in the developer console as well as during a jitterbit upload. I found a note at the bottom of the help sheet here that does make it sound like it's expected behavior.

After you change a record’s owner, the previous owner’s visibility reverts to the default sharing setting unless that user is on an account or opportunity team. For example, if the previous owner of an account is on an account team, that user has Read Only or the access specified in your organization-wide default for accounts, whichever is greater. The previous owner’s access to related records remain the same. This behavior is the same for opportunity owners that are members of an opportunity team as long as you change ownership using the API. When you change ownership of an opportunity within Salesforce, you can select the access level you want.