When you create a vertical cable to ride, like so:

riding it moves the player into the pillar, where he is then stuck. To aggravate this issue, even if the blocks that would block/suffocate the player are removed, the player is stuck in the air, glitching back and forth, which, as far as I can tell, can only be fixed by quitting and reloading/rejoining the world. (can't even fly away in creative)

I don't know if this issue is exclusive to purely vertical cables, but I didn't find any others.

IE 0.12-82
forge x2709
no other mods