What is happening to my washing?

But its not a one off Bags it seems to happen every few weeks and not always with new things. It has to be something to do with the stuff I put in the machine or the way I am using it. I can't try using something different as it doesn't happen often enough for me to know if it has worked or not. I could stop using the water softeners but would then be risking damaging the machine.

I have found that at times powder does not all dissolve in lower temp. washes and can then land on the fabric as I have had the odd time when there has been telltale powder left - I now use a liquid which I put into the usual drawer in the machine. The stuff I have for doing dark washing has always been a liquid.
Such a nuisance that happening on a good garment.

Hmm. Puzzling. Is it a really good quality shirt? If so, you could try taking it back and explaining that it hasn't stood up to normal wear and washing.

I'm nearly at the end of a big pack of Surf but I just buy whichever is on offer!

It sounds as if something like bleach has got onto the fabric. This could be some ingredient in the washing powder. What kind do you use?