/A learner/
1)"When I came home they were alredy kicking this issue around for half an hour." Doesn't "before" interupts action as well?
If we slightly rearange the sentences and put it like this 2) "I came home. They were already kicking it around for half an hour."?
The is that prescribed grammar suggests the past perfect progressive with "half an hour", "thirty minutes"???
At this moment of speaking, (not in the past) the present perfect continuous tell us about the fact that
they have been kicking this issue around for half an hour.
If I cut in (now) they will either stop or continue. But there is no time distance between their kicking around and my cut in.
If I say, 'They have kicked around this issue for half an hour.', it means that they have done it in the past. When? You can't make the right conclusion from that sentence. But what for sure is, is that I can't cut in at the moment of my speaking even if I say, "They have just kicked around this issue for half an hour." (I am able to cut in if I came just a bit earlier.)
The same is with the past perfect continuous used for an action or event that started to happen in the deep past.
They had been kicking this issue around for half an hour when I (did really) cut in.
They probably continued their kicking around. It is possible that the action be continued at the moment of my cut in in the past.
But if I say
"They had kicked this issue around for two hours before I came."
it means, for me of course, as I am not a teacher, that they had stopped before I came. There is a time distance between their kicking around and my coming. (I couldn't have cut in actually)
"They had
just kicked this issue around for two hours before I came in." doesn't mean that they stopped because I came in. The time delay, mentioned, is reduced almost to zero. Please notice that I have said almost to zero and not to zero. There is always a time distance even infinitesimally small.
In addition
"They were talking
for two hours when I came." is not possible. (the past perfect continuous ought to be used)
But
"They were talking when I came." is possible, for me, a learner. (No time limits for the past continuous tense)
This is how I see the matter. (At the moment.;-)
)
P.S. I was wrong when I said that I would accept using the past continuous tense instead of the past perfect continuous in some circumstances and by some way.