Problems with IPN validation with Paypal_lib

[eluser]Unknown[/eluser]
I have problem on IPN validation, and I don't understand why...

Some times, for some users, i receive in log, FAILED for ipn_validation, but money are transferred to my paypal acc, and in paypal account ipn history, all requests are valid.

I double rechek the code,
replace eregi, with stristr, because of php.net says it will be deprecated...
all data is transfared in UTF-8.

Please, any ideas?

or maybe some one had problems like that?