I don't know if someone already experienced this bug.I'm unable to use ext4 with antix(i haven't tried another distro yet) because the filsystem gets corrupted quite often and easily.I red on the internet that it is a bug present in 4.0.x linux kernel and it shows up only with RAID disks.It seems like that this bug doesn't affect only RAID disks but also usb sticks.Can someone help me or explain what's happening with ext4?

As you say it is/was a bug in the kernel code which is at 4.0.6 at least now.

There is an antiX-4.0.5 kernel (and 4.0.4) in the repos. The raid/ext4 issue was supposed to have been addressed in kernel 4.0.4 and later.