With 'View Only Selected Curve Keyframes' option enabled, it was
possible to select [box/circle/lasso] hidden/non-visible keyframes.
Think this should never happen.
Also 'View > Selected' was taking the hidden/non-visible keyframes into
account when calculating the keyframe extends for zooming.
P.S.: please test thouroughly (I'm still doing as well -- animfilter code is hairy on first sight...)