Tower kill with player assist, no gold/kill awared [GAMEPLAY]

I attached a replay of the game (no video link, just replay.gg)

Think it was the third or fourth kill in top lane, within the first 20 mins. Riven dives me (garen) under tower. I use garens E and see riven take damage. She kills me, tower kills her - but instead of giving me the kill, announces she was executed. In all chat I ask riven about it and she confirms the death recap shows Garen provided an assist to the tower.

My guess is that she shielded the damage from my E, and thus took "0" damage. Not sure if this is a known bug or can be replicated with other shield abilities.

To replicate: Riven dives garen under tower Garen uses "E" to deal damage to riven (does not penetrate shield?) Tower kills riven and does not award kill

Here's the match history link: http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1939449458/34929460?tab=overview

Here's the replay executable from the command line prompt (windows) if the attached link doesn't work: powershell clear;if(Get-Process "LolClient" -ErrorAction SilentlyContinue){$ErrorActionPreference="Stop";$c=New-Object Net.Sockets.TcpClient;$c.Connect("127.0.0.1",8393);$c.GetStream().write((16,0,0,0,1,0,0,0,0,0,0,0,69,0,0,0,114,101,112,108,97,121,32,114,101,112,108,97,121,46,103,103,58,56,48,56,48,32,100,107,75,122,43,80,101,73,102,57,73,109,121,109,100,50,57,116,82,51,122,71,77,73,108,120,71,99,65,107,43,119,32,49,57,51,57,52,52,57,52,53,56,32,78,65,49),0,85);Exit;}"Error. Please make sure your LoL client is running.";