When switching back to a regular build mode from Spectate, the arm disappears.
The arm was supposed to come back
It was still invisible
1.In creative, type. /gamemode 3 (Spectate)
2.Switch back to /gamemode 1 (Creative)
3.Watch as you interact without an arm.
Environment
Windows 7 - Latest Java Version
Confirmed for me using vanilla singleplayer using 14w05b.