Using layer mask, image is still visible even when painted out using black brush

When I am using black on a layer mask to paint away parts of an image I noticed that it leaves the image transparent in the background. This is when my layer and brush are at 100% opacity and the layer and brush mode are normal. I have been using layer masks for the past 2 months and just noticed this issue last week. The only way I can completely paint away the image using a mask is when I click the mask channel and paint with that on, Is there another solution to this?

Your default black swatch has probably changed, press the "d" key to reset it

In the colour picker, do NOT set the black as CMYK colours ( 0/0/0/100 ) use RGB ( 0/0/0 ) instead

thank you thank you!

this same problem has had me stumped for weeks. It just started all of the sudden like Hannah stated.
I was making the mask color CMYK 0000 but never tried RGB ones

thanks

D Kelly
artnmurals.com