It's possible for a block's "powered" state to become 'stuck' upon loading it from a structure block.

To recreate:
1) Place a Save structure block that will save one block: a pressure plate on top of it.

2) Jump on the pressure plate to activate the structure block

3) Load the resulting structure elsewhere. The pressure plate's "powered" state will be stuck to "true" permanently, and cannot be changed without using a debug stick or breaking the block.

Similar things can be done with other blocks, mostly (but not always) those with "powered" block states:

• Buttons and pressure plates remain permanently activated as described above if saved while powered. If saved while unpowered, they operate normally.
• Repeaters, comparators, fence gates, note blocks, trapdoors, doors load their "powered" state as it was saved and won't correct themselves until given a further block update.
• Redstone lamps do the same as repeaters and the like with their "lit" state instead of "powered".
• Command Blocks and Structure Blocks function as repeaters/lamps–if powered when saved, they will think they're still powered when loaded up (despite not having a corresponding block state) and will not correct this until given a block update.
• Redstone wire will load normally if there was a different block in that spot before it was loaded. If, however, it loads into a block that was already redstone wire, it will load its "power" state as it was saved, and will not correct this until given a block update, though other states autocorrect as they should.
• Tripwire hooks load as attached and powered if saved that way even if no string is present in the new position; normal block updates will not correct this, though reconnecting a full tripwire will do so.
• Observers are hard to save with proper timing, but I have managed to create 'stopped' observer clocks (and 'double-time' observer clocks) by saving two observers pointing into each other and loading them repeatedly.
• Redstone torches, levers, and all rail types load and function properly.