hmm --
I am just experiencing this, and have experienced it in non-profit world where I mostly work, even at level of writing articles/books.
Partly it's due to enthusiasm and so project grows in ambition, but I feel every now and then one should, as diplomatically as possible, draw the line.
And keep one's rights as a free lance writer.
Even work for hire, sometimes the employer encroaches.
A friend told me that she was asked to turn in all photos she took on her own on a work trip. She refused.
We should be like doctors and dentists. "Would you like to write the check now?" (Before anyone touches our teeth etc). Why do people think we can write (or paint) effortlessly and without any costs, in our sleep.
