This is a question I'm asking just to answer it myself, but of course other answers are welcome.
Answering this question about the curious property of aburrido as an active adjective (instead of the passive meaning one would expect from a passive participle), I gave some examples of morphologically passive adjectives behaving not quite the part. A comment made me realize that Spanish students are being taught the simple rule of thumb «estar aburrido means "to be bored" and ser aburrido means "to be boring"». Searching further it appears that aburrido is not that rare: callado, cansado, considerado, divertido and others (like molesto, which is not a participle but is close to one) share this behavior. Yet it is possible to say (against the rule):
- El partido está aburrido. "The match is boring."
- La fiesta está divertida. "The party is fun/entertaining."
- Este trabajo está muy cansado. "This work is very tiring."
- El calor está realmente molesto. "The heat is really bothersome."
That is, estar + passive participle yields a clearly active meaning. So how do we know which meaning to ascribe to an adjective like aburrido, divertido, cansado, molesto, when coupled with estar? And why does this happen?