Before any noun - this is explained in the notes for the section 'Numbers'. The final letters of pump, chwech, cant should normslly be dropped before nouns.
Yes, as explained in the notes on 'Numbers'. It should be pum iâr and that correct version will be presented about half the time at the moment until we can get rid of the error.
Ha, and when I reloaded this page I indeed saw pum iâr without -p!
I always thought the sentence on the sentence discussion page was fixed, and the probability only applied to exercises.
Edit: now "back" to pump iâr. And reloading the page makes it switch back and forth.
So it does seem to switch on sentence discussions as well. Huh.