It seems that when you attack and then try to block immediately, the attack animation has to end first before you can block. This way you hold the block button but the character is not blocking. If it's by design, it doesn't add much to the gameplay but is quite annoying that you have to spam block button and when you see character blocking, you hold it. (played with keyboard+mouse).
Any chance to get any video settings available? I'd love to lower the resolution :)