Never come across a logbook like that.
If you're flying in IMC, you're obviously flying in IFR conditions, so log that as such.
You don't need to be under an IFR Flight Plan to be able to log IFR. eg - If you're going somewhere VFR and the weather closes in, you then become IFR, so if you're really keen for those hours, you'd note the time you went IFR and log that.
As for a bog standard public transport flight, I wouldn't log IFR time blocks to blocks, after all, you don't taxi under IFR conditions. I only log airborne to landing times as IFR.
IF, to me, would suggest Exercise 18. ie Flying with sole reference to the instruments, but this could be interpreted several ways I'd imagine.
Hope this clears up some of it.