Just to follow up, I'm afraid as we have quickly become popular, we have recently become a target of people lying. Just yesterday a handful of people came into our IRC room claiming to have lost BTC and then not being able to provide any proof about it.
While we cannot stop people from spreading misinformation, I would just like to advise users that they are welcome to try us out and see for themselves that everything works fine. 99% of our users have never had an issue, but if you do think something strange has happened then please open a support ticket. We will do our best to assure you and solve the problem if there is an issue.
About this, dont know is it the same reason but my friend lost 3btc, he was sending them to mintpal deposit. After researching what was wrong he noted that his bitstamp ticker extension (google chrome) had been hacked and it changed deposit addresses for mintpal. Noticed when opened page with ie and had different deposit addresses. We dont know is it wide problem with this extension or was it just single hacking but this might be reason for "losing btc in mintpal"