About a year ago I noticed this happening and posted about it. It eventually got fixed... but now it's doing it again. Normally you can 'work down' a spell ward using Dispel Magic or Greater Dispel Magic... but when it's glitching you will see the dispel reduction amount (random 1-4 levels) upon cast, but the ward only drops a single (or zero) level. Another cast will most often reset the ward to its original strength regardless of the dispel cast results. Considering how prevalent Wards are in the Underdark.... this gets REALLY aggravating while running content at challenging levels.
Please fix this, no idea what you did that broke it again, but here we go again....