TL;DRCurrently, if the player shift-clicks to place a blueprint while their mouse happens to be over an existing power pole, all the pole's connections are removed, which is almost never the desired behaviour.
What ?The 'shift-click a power pole to remove all connections' functionality should be disabled if the player is holding a blueprint.
Why ?I have a standard blueprint I use for my main rail lines - two lines of track 4 spaces apart, with rail signals at regular intervals and big electric poles between them. This blueprint is 62 spaces long, with power poles at each end and in the center, since that makes it easy to tile. However, this means that the center pole is at the exact center of the blueprint, which means if I'm trying to align a new copy of it with an existing line, my mouse will be centered on the last existing power pole of the already built section. If I'm placing the blueprint with shift-click so that rocks and trees are automatically cleared away (which I almost always am) then I end up removing the existing wire connection on the pole I'm aligning with.
This can also happen when placing other blueprints that overlap with existing construction. Re-placing a mall to set new assembler recipes as you researched them? Copying a section of an array to extend it? Better hope your blueprint doesn't happen to have a power pole at the center.