I've tested the mentioned feature of build 4060:

POP3: Added workaround for Gmail's POP3 service which makes retrieved messages invisible next time.messages invisible next time.

And it seems to be working right. I've performed the following steps:

1) Sent some e-mails to my Gmail mailbox and checked they are visible in Inbox on the Gmail web.

2) Listed all messages from the Gmail mailbox using POP3 protocol like in the mentioned post:

Pop3 client = new Pop3(); 
client.Connect("pop.gmail.com", Pop3.DefaultImplicitSslPort, null, Pop3Security.Implicit);
client.Login("username", "password");
//UNCOMMENT THE FOLLOWING LINE AND THE COMPONENT WILL WORK IN THE OLD STYLE (WITHOUT WORKAROUND ADDED IN BUILD 4060)
//client.Options = Pop3Options.DisableGmailRetrieveWorkaround;
Pop3MessageCollection messages = client.GetMessageList(Pop3ListFields.FullHeaders);
foreach (Pop3MessageInfo msg in messages)
{
    MailMessage fullMsg = client.GetMailMessage(msg.SequenceNumber);
    Console.WriteLine("From: " + msg.From + ", To: " + msg.To + ", Subject: " + msg.Subject);
}
client.Disconnect();

3) Executed the code again and again - all messages were listed all the time.

So why would your messages remain in your web Gmail mailbox even if they are no more visible through POP3?

A) If there were some older messages in the mailbox, which have been once touched using the old version of POP3 component (build earlier than 4060), they have been marked as "retrieved by POP3" an they will never be available through POP3 protocol even if using the newest POP3 component. You can reset it according to the following post.

B) If you have deleted the messages using POP3 protocol and your Gmail settings for POP3 deleting is "keep Gmail's copy in the Inbox", the messages are still visible in the Gmail web even though they seem to be deleted through the POP3. To change settings for POP3-delete see the following post.

If none of this alternatives describes your situation and you are still retrieving 0 messages using the Rebex POP3, please write us again and describe your situation in more details (a scrap of code would be helpful).