All of this is made on purpose.
Such issues have been already fixed in one of the russian patches some months ago. Since the chance is 20-30% to evade EVERY attack (not 1 in 3 or 1 in 5), sometimes it used to proc way too often. So, like we have it here, they made it that if the unit evades the previous attack, it will always be hit by the next one, including retaliations.
The Guardsmen evade 30% of the attacks when they lose part of their troop. Others, like sea dogs, have it built-in. Dryads and Demonesses only evade against male chars.
So, yes, everything is on purpose. Besides, you can always make use of the evasion and laugh at the stupid swinging enemies who hit for nothing
