Case 1:
When a current passes over a block A, which has one block of space in between it and a piston directly below, and the current was at that height level for at least one block before block A and continues after block A for at least one block, and lastly the current gets close to the piston, many weird things happen (Picture 1).
If the piston is touching a block B and the current isn't touching the block on one of its sides, the piston doesn't move, but when the current does touch the piston, it extends (Picture 2) ! No current is touching the piston whatsoever.
If you get rid of any redstone but the redstone above, the piston stays extended (Picture 3). If you do this, then delete the redstone above, the piston stays extended (Picture 30). The only way to un-extend it at this point is to place or remove blocks around the piston.
If you only delete the redstone above the piston while it's extended, only then will it un-extended (Picture 4).

I worked with the bug and found the same things happen if the block isn't there, and the same solution is found (Pictures 5 & 6).

Case 2:
I also found that if the block before the block A is at the same level but the block after is at a lower level (Picture 7), the same thing happens, but the piston un-extends differently (Picture 8). To un-extend the piston, you must stop the current from going over the piston, and then place or remove a block near the piston (Pictures 9 & Picture 15).
I played around with this more, by making the situation occur again, and then placing or deleting blocks in different spots around the piston, and found that the same thing occurred (Pictures 10-14).

Case 3:
If the current raised one level to reach the level at block A immediately before the piston, and then continued after the piston for at least one block at that level (Picture 16), the same things happens as Case 2. The current must be stopped from reaching above the piston, and then placing or removing any redstone around the piston causes it to un-extend (Pictures 17 & 18)

Case 4:
If the block before and the block after Block A are both one level below the height of Block A (Picture 19), the same thing happens as Case 2 and 3 (Pictures 20 & 21).

If the current begins at block A, this doesn't happen (Picture 22).

If the current never goes over block A but gets close to the piston, this doesn't happen (Picture 23 & 24).

This bug effects both sticky pistons and normal pistons (Pictures 5 & 25).

If a piston experiences this bug, and another piston is placed next to it, while still under the current, this new piston will also extend (Picture 26) and the height of the block above the new piston doesn't seem to matter (Picture 27). Destroying the redstone above the rightmost piston will un-extend all of them (Picture 29), but if a more left one's redstone is destroyed, only the pistons down that line will be un-extended, but not the ones before (Picture 28).

Case 5:
If the blocks before and after Block A are above it's height (Picture 31), the piston is subject to the un-extending techniques in Case 1: either delete the redstone above the piston (Picture 32), or if you remove other redstone (Picture 33), remove first the redstone above the piston, and then add or remove redstone next to the piston (Picture 34).

There seems to be more factors to this bug, like the amount of redstone on the ground leading to the piston. In all cases above, the order I state things is the order I did them in.

I hope my in-depthness will help to resolve this bug, for as a redstone enthusiast it pains me to see redstone bugs, especially when they are affecting my most recent project.