If USE contains webkit then mail-client/claws-mail-3.9.1 depends on webkit-gtk and libsoup-gnome. Depending on just libsoup-gnome breaks dependency resolution if the installed libsoup >= 2.24. Reproducible: Always
Created attachment 347982 [details, diff] patch for ebuild to depend on either libsoup-gnome or libsoup
Thanks for the information. Fixed in CVS.