Reimplementing QFtp and "Cannot mix incompatible Qt libraries" error

[ultr]

I'm trying to reimplement QFtp class to add some methods I need to it.

Everything compiles and seems to work
but when I create a new instance of my QFtp in run-time
program exists with "Cannot mix incompatible Qt libraries" error.

I use sources of the very same version of Qt I have in my system.

Simple test code attached.

Thanks for help or any suggestions.