Job Task Line / Dimensions

Can anybody tell me, the relevance of Dimensions on Job Task Lines?

It seems to me, that when I attach default dimensions to Job Task Lines, and later reference the job/job task combination in a Job journal or Time sheet, the default dimension seem to be ignored.

It is not transferred from the Job Task to the Job Journal Line.

I have tried this in 2009 R2 and 2013.

Any ideas?