Nice catch. Its not bug your getting different results for same implementation because public functions and external functions will handle memory differently. In solidity public function immediately copies array arguments to memory. When your coping values in to memory it will padding with 32 bytes. 

    EmitString(logme)


>0x00000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000006676c69746368

As per EVM documentation `EmitString(logme)` **logme** is string type saving or representation would be 1st 32 bytes(32*2=64 chars) will represents location of string 

> 0x0000000000000000000000000000000000000000000000000000000000000020 = 32

Now pointer will move to 33bytes to next 32 bytes is length so length is 

> 0000000000000000000000000000000000000000000000000000000000000006 = 6, i.e next 6 bytes are data.

> 676c69746368 hex representation of string.

Memory representation of any bytes is padded with multiples of  32 bytes. Thats a reason you are getting `676c697463680000000000000000000000000000000000000000000000000000`

Where is case of external functions can read directly from calldata. What is values your passing it will send same thing to the network. So thats reason you able to see only `676c69746368`

Memory allocation is expensive, whereas reading from calldata is cheap.

https://ethereum.stackexchange.com/questions/19380/external-vs-public-best-practices?answertab=active#tab-top