Mistery of reading GMail inbox by JavaMail via POP3

Today I’ve got a very strange problem reading Gmail INBOX via POP3.

Yesterday I was able to read all of the e-mails, but today something strange began to happen. In the reality mailbox had five e-mails, application was able to read four while the JUnit test which has exactly the same flow was able to read only three of them.

Went to the setting of the POP3 – it looked like:

So POP3 is enabled. Once I’ve selected the first radiobutton and updated changes – I’ve started recieving all five messages. Frankly speaking I don’t know why this happens. Anyone does?