I looked into PyS60 source and in ext/inbox/inboxadapter.cpp is a function GetMessageL and there are these lines:
And in ext/inbox/inbox.h the constant KMessageBodySize is set to 512.
// Check length because message is read to limited size TBuf
if (length >= KMessageBodySize)
message.Append(richText->Read(0, KMessageBodySize -1));
I think that this is the problem, but I don't know why the size of const on my python i 256.I also don't know why it's 512, it's only about 3 smses which is not so many..