Within any gtk3 app that includes editable text/input boxes (don't know the exact name/label of the widget type in gtk+ terminology, sorry), e.g. the URL bar in epiphany or the zoom level box in evince _in a wayland/weston environment_, text selections don't "stick"; as in the selection, generally indicated by inversed text foreground/background colors, isn't preserved after the left mouse button is released.

Clearing parts of the URL bar text content in epiphany is, however, possible if the backspace/delete key is pressed whilst still holding the mouse button.

Double click selection (used to select either single words or everything in the widget) also doesn't seem to be working.

Text selection within the WebKit part of the window (epiphany) seems to be working quite perfectly though.

setup:

Arch Linux x86_64, 
gtk-3.10.5-1 / wayland-1.3.0-1 / weston-1.3.1-1

(epiphany 3.10.2-1 / evince 3.10.3-1)