Context

I put a saddle on a pig, then I gave him a nametag by right-clicking. This caused me to mount him and made disappear the nametag from my inventory. The pig was named.

What happened

By right-clicking a second time, the nametag came back in my inventory but the pig was still named.

What I expected

The nametag shouldn't have come back.

Probable cause

It might be caused by a conflict between two actions lead by a one command (right click).
Also it looks like server protection. You know, when you place a block where you are not allowed to, the block seems consumed but you get it back when right clicking anywhere.

Note about affected version

It happened in vanilla 1.7.2 but I couldn't choose it in the box above.