Don't know if this is OT or related...

For me it was Master settings > Primary settings | General | Censor | Stop spam (that I lost.)

I may post more on this tomorrow (it's late here now), but...

Two days ago, I decided to change my cookie expiry time (due to the problems with people staying logged in).

As a result, I was logged out of the admin CP. That was scary!
I tried on different PCs - still the same. Then oddly enough, I managed to stay logged in long enough to notice that the cookie path was blank (instead of the default '/' ).

Further investigation revealed that a big 'chunk' of my config file was corrupted (actually - the array values were empty).
This is clearly very different to the zero byte problem previously encountered.

It looks like most of my admin cp 'primary settings' were lost. However the rest of the file remained in-tact.
At that point I was able to realise that the main administrator user was blank and was the reason for me being logged out.

I've been too busy to establish what is related in the corrupted array, but after my zero byte config.inc issues, I am feeling somewhat paranoid/ vulnerable to say the least.