The bug

Selectors in the text of the command /me (in previous versions also /tell, /msg and /w) are not resolved when an operator uses the command. They are however resolved when the command sender is not a player like for example an entity, a command block or a sign.

How to reproduce

Use the following command as operator

/me Closest player: @p

Code analysis

Based on 1.11.2 decompiled using MCP 9.35 rc1

This feature was probably disabled as a fix for MC-43984, but for all players. This can be solved by having the methods net.minecraft.command.server.CommandEmote.execute(MinecraftServer, ICommandSender, String[]) and net.minecraft.command.server.CommandMessage.execute(MinecraftServer, ICommandSender, String[]) call a method which calls the method net.minecraft.command.CommandBase.getChatComponentFromNthArg(ICommandSender, String[], int, boolean) with the boolean parameter value being if the player can use selectors.

public static ITextComponent getChatComponentFromNthArgIfCanUseSelector(ICommandSender sender, String[] args, int index) throws PlayerNotFoundException, CommandException {
    return getChatComponentFromNthArg(sender, args, index, sender.canUseCommand(1, ""));
}