Security Settings won't reset "Launching applications and unsafe files"

Hi,

I'm using Windows 8.1 update 1 with IE.

I found a very strange problem,

If I changed the setting of:

Security tab-> Internet -> Custom level -> Miscellaneous -> Launching applications and unsafe file,

for example, I changed the setting from default "Prompt" to "Enable",

Then I tried to reset all setting to "Medium-high(default)" at "Reset custom settings",

The setting I changed above never goes back to its default setting, it keeps the status"Enable".

All other settings I changed would be reset normally but only this one refuse to be reset.

B.T.W,  I noticed this because somehow my IE refused to allow me download any exe file, even though I tried to reset the security setting. The only way which could let me reset this is to click the reset button in "Advanced" tab.

I don't know if this is intended or a bug or something wrong with my PC, but this is dangerous I think, because it made me believe that I have reset my security setting but actually not.

I tried to scan my PC with windows defender and MalwareBytes and found no threat. Windows update is also in an up-to-date state. I also tried to launch IE as admin then reset the security setting and with no luck.

I'm worrying about my PC is getting some kind of virus which caused this problem, so if any information will be appreciated.

Thanks in advance!