Minecraft 14w17a, Minecraft 14w21b, Minecraft 14w25b
Mac OS X 10.9.2, Java 7 Update 55
This bug doesn't affect the original default resource pack, but it does affect other resource packs, such as the 32x32 Faithful Resource Pack by Vattic. 1.7.x (or 14w11b) Resource packs running 14w17a or later will have the redstone dust line rotated the wrong way when connected to another.
To fix this issue, try going inside the folder of the resource pack, and rotate the redstone dust line 90 degrees with any editing program.
WARNING: If you're not running the 1.8 snapshots, you might need to rotate the redstone dust line back to the way it was when the resource pack was created.
If anyone is experimenting with this problem, read the Moderator Edit.