I don't know what dictionary is being used here, but rabbiter and looper were both rejected despite being in the UK and US Scrabble Words lists. That's immensely annoying.
I mean, maybe not immensely annoying in the general scheme of things... :-)
On the scale of how annoying things are, it's somewhere between the squeaking noise my office chair makes if I lean back too far and the threat of global thermonuclear war.
Also hackable and some other -able words were not accepted.