Comment 10 for bug 1661556

Found a workaround by user BradPitcher here:
http://elementaryos.stackexchange.com/questions/10529/ctrl-whatever-and-shift-whatever-require-double-tap

This bug was introduced in 3.18.10 and is fixed in 3.18.11 with this commit. You can wait for the updated package to come down the pipeline or make the change yourself as I did:

% sudo apt-get install build-essential
% sudo apt-get build-dep epiphany-browser
% apt-get source epiphany-browser
% cd epiphany-browser-3.18.10
Make the changes from the commit I linked to: edit src/ephy-window.c, make a new line after line 882 and put the code return TRUE;
% dpkg-buildpackage -us -uc
% cd ..
% sudo dpkg -i epiphany-browser*.deb
% sudo apt-get -f install

It did the Job :)