it's not necessarily a bug. from all i've seen (haven't heard anyone give any proof or explaination about blink really), it looks like blink calculates a vector along the surface based on your facing. in the case of water, it's just that.
at the entrance of some building or most bridges, the world geometry seems to have been made in multiple pieces. that is, they aren't a part of the surface you're standing on. seems that the spell's calculation just stops you at the "edge" of your current surface because there's no way for it to continue to a totally different object. when things like lamp posts or rocks are scattered onto and then clipped with the ground surface, they make a hole there and this just creates a new "edge" or "end" that the spell's function reacts the same way to. it's to prevent you from blinking through the "world".
if this is the case, then it's not bug with the spell, it's just a difficulty in using it. blizzard's response then would be "work on your aim" =\
i always thought (since mages and the sorceress have always been just about identical anyway) that they should just let us point and click to teleport freely within our field of vision. they could, for instance, charge us mana per unit of absolute distance displaced...