Using the /fill command does not always update the surrounding blocks. They can be made to change by manually causing a block update.

[In the picture above, I used the /fill command to fill in those redstone blocks]
Not only redstone dust is affected. Command blocks do not update, water does not always flow, etc.
Oddly, blocks will be affected if they are touching one of the 2 blocks used as the corners
used within the command, but only then.