Look closely between the seam of the wallpaper in the top photo. You can see little crumbly things. In the second photo, the issue is even more pronounced; you can see bits of paint coming away from the wall and stuck to the back of the wallpaper.
This is in the upstairs bathroom of a 1950 house in central Houston. Over time, compounded by humidity, poor air circulation, poor air conditioning / heating, and possible influences from the outdoors, various layers inside the wall have let loose of one another.
What are these layers? Originally the walls were probably painted with oil-based paint. Over the years, layers of latex paint, gloss paint, joint compound, dust, and etc. were piled on, probably without proper prep between coats.
Some of these materials are not compatible with one another, and, over time and with stressers like humidity, along with the tension / torque caused by drying wallpaper, they can let go of one another.
If just the wallpaper has come loose, it can be pasted and re-adhered. But we’re seldom that lucky. When the wall itself is coming apart, there is no fix, other than to scrap everything down to the original drywall (huge mess) or go over everything with 1/4″ drywall. Sometimes a liner paper can be used with success.
In this case, the homeowner had me repaste the few loose areas of paper, and then chose to live with the other visible cracks, chalking it up to an old house full of character and quirks.
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