[otrs] Loosing attachments in otrs 3.0.4

Hi, I am using otrs 3.0.4 for cca 2 years. I am downolading e-mails from MS Exchange 2007 server over pop3. About 3 month I can see sometimes, that some message in otrs lost attachments but if client sent message directly to me, everything is allright. Attachments are small, in every case (but till this time) are pdf. I cannot simulate it so I dont know i which case are attachments lost. Where I should look for mistake? Thank you Radek