Transaction missing on Etherscan?

When I download all of the internal transactions from Etherscan through the web interface, it appears to be missing one transaction. This is because the sum didn't sum to my wallet balance. I made sure the dates included all transactions that occurred. I am using the "CSV export" feature on etherscan.io.

When I download the transactions using the API:

https://api.etherscan.io/api?module=account&action=txlistinternal&address=<MyAddress>&sort=asc&apikey=YourApiKeyToken

The missing transaction appears (the sum reaches the wallet balance and the missing transaction hash appears in the list). Why would the web interface exclude a transaction? Is this a bug?