Sounds like you have the Standard Shield set to High not Normal the default setting ?
Just opening a folder shouldn't cause it to be scanned, unless winwall access all images.
It also sounds like you haven't set the exclusion in the correct location or the path is wrong.
What did you enter in the exclusion ?
add it to the Standard Shield exclusions list:
Standard Shield, Customize, Advanced, Add that is the one responsible for on-access scanning.