I've noticed that Wayland only supports a single selection. GTK+ uses two selections, CLIPBOARD and PRIMARY. The problem with the wayland implementation is that it totally ignores clipboard names with the result that CLIPBOARD and PRIMARY interfere with each other.

Try this:

1) open the clipboard example in gtk-demo
2) enter 'abc' into the first entry
3) click Copy (now the CLIPBOARD selection contains 'abc'
4) replace the contents of the entry with 'uvw'
5) select this text ( now the PRIMARY selection 'uvw')
6) click Paste
7) expect the second entry to be filled with the CLIPBOARD selection, but it reads 'uvw', which is the PRIMARY