I don't see that Windows Defender can be removed in Programs and Features.
I'm on a system now that has MS Security Essentials, and Windows Defender is turned off.
MsMpEng.exe is running, but that is for MS Security Essentials version 4 (not Windows Defender).
The folder for Security Essentials version 4 is C:\Program Files\Microsoft Security Client\
I always see all entries because i normally use Process Explorer (not Task Manager).
I think the process you see running is Security Essentials (not Windows Defender).
What is the folder for your MsMpEng.exe?