What happens if only droptol is set in ilu?

I realised, that when I was using ilu with only setup.droptol set, then I got wrong results with pcg using the lu decomposition as a preconditioner. Analysing the problem I realised, that the droptol which I set did not make a difference at all and the ilu decomposition was unusually fast. However, if I also set the setup.type to 'ilutp' (which should be the default anyways), then I got the correct results, the ilu took a reasonable amount of time and the specified droptol was considered. Is that a bug or am I doing something wrong?