Originally Posted by double_e5
I don't think a month would be an issue, but soapy flavors can come from the fatty acids in the trub breaking down.
Another thing could be as simple as not washing/rinsing your glasses very well.
In Palmer's book he states something to the effect that leaving in Primary more that 3 weeks can result in soapy off flavors. I was a little worried about that as I left mine in my primary for almost 4 weeks.
That said, I know a lot of people say they've left theirs on the trub for months with no ill affects.
FYI - here's the quote from Palmer: "Leaving the post-primary beer on the trub and yeast cake for too long (more than about three weeks) will tend to result in soapy flavors becoming evident. "