I've noticed that too Dopp. O the flip side i've found that you don't need Pikemen in Guard Mode for the to brace and that units in Guard Mode take a LOT more losses from a charge so that might be somthing to check.

Also, once sheild infantrys defence gets high enough, they are amazingly resistant to formed charges. Any Sword and Sheil unit with a defence of more than 20 can take a Mailed/Feudal Knight charge with much lower losses than any spear unit, except Papal Guard.