Tab complete does not work in command block or chat after execute command

Tab autocomplete in a command block or chat does not work in the command after an execute command.

How to replicate:

1. Open up snapshot 16w02a and give yourself a command block (/give @p command_block)

2. Write this command in there, but do not close the command block:

/execute @p ~ ~ ~

3. Now, after that command, start writing the first part of another command, for example write: /part and hit tab. Nothing happens.

This appears to happen to everything after the execute command and is annoying when writing commands oriented around /execute.