I have encountered this too. It seems like on the tactical map in .8 that unless you click on the exact center of the tile it won't work. I didn't notice it in FE or .75, but it might have been in earlier versions too, but I didn't notice it as much. I have pictures backing this up.
https://dl.dropboxusercontent.com/u/77858773/LegendaryHeroes_1365957184.jpg
Trying to use crushing blow against a river slag in the above photo. Since I was clicking the exact center of the hex, it's saying the target is out of range.
https://dl.dropboxusercontent.com/u/77858773/LegendaryHeroes_1365958222.jpg
In the above photo I am clicking in the enemy's tile, but once again since it's not the exact center, the game doesn't credit me for targeting an enemy.
This is one of the most frustrating aspects of the game for me.