using thunderbird as a mail provider

have been using this for a number of years now with no problems until I ditched my OZ provider [no longer needed] and stayed with yahoo and a few other subsiduaries floating about. everything still fine until recently and then emails were not being transfered from yahoo to thunderbird with the explanation -- [client bug] select command not valid - very friendly indeed

well to cut a long story short this has been affecting dozens of persons and someone finally found away around it which really just boiled down to clipping off the end of your yahoo address in the thunderbird file. 

why do they do these terrible things???

Because they are stupid?