Ubuntu 13.10 64bit
Java(TM) SE Runtime Environment (build 1.7.0_17-b02)
After using F5 in spectator mode the arm stays invisible until F5 is used again. Switching to spectator mode without using F5 doesn't make the arm invisible.
Steps to reproduce:
1. Switch into spectator mode.
2. Press F5 three times.
3. Switch back to creative or survival.
4. Observe the missing arm (see screenshot).
5. Press F5 three times again.
6. Observe arm being visible again.