Force Field immunity does not work properly. Although the "Spell Immunity" message will be displayed, the force field is still created around the spell-warded target, preventing movement.
The same behavior can be observed with Crushing Prison. The "Spell Immunity" message will appear, to indicate negation of primary damage by Crushing Prison spell, but the prison is still created, immobilizing the spell-warded target.
Some spells' secondary effects (Freezing, Movement Speed Decrease etc.) are still applied, only the primary effect (i.e. actual damage) is negated. Please refer to the talk page for technical details.
A fix for this, regarding hostile effects, is available here.
Casting Power of Blood spell Bloody Grasp while under the effect of Anti-Magic Ward (i.e.: you cast it on yourself) apparently avoids the -20 health loss of Bloody Grasp.
On difficulty settings where friendly fire is active, this can be used on a team member who is surrounded by enemies and then they can be subsequently targeted by area effect attacks without ill effect (barring above issues).