It's difficult to place rope ladders above while hanging onto rope ladders.

[poncho]

I dug straight down through one by one block hole. after finishing mining, I tried to place the ladder by pressing the Shift key and the right mouse button together, but before I could place it, the Shift key made me climb down.

[LadyWYT]

I typically either dig a little bit, drop down, and then place the ladders, or hold space in addition to shift + right-click to make it a little easier to place the rope ladders while I'm still hanging on to them. It's not 100% foolproof, but that's one of the main disadvantages of using rope ladders instead of standard ladders.