I've seen several people report this problem in different forums.

# Faulty Behaviour #
- For the life of me I couldn't figure out why I suddenly couldn't search in my editor or web-browser after switching to xfce4, `ctrl+f` didn't "bite".
- None of the shortcuts in the list where one of the "disappearing" ones (only the pre-confed standards that came with xfce4: opening display-settings with Mod4+p, etc...)

# Finding Culprit #
- using xev and then the `KEY1="Control";KEY2="f"; xdotool keydown ${KEY1}; xdotool keydown ${KEY2}; xdotool key XF86LogGrabInfo; xdotool keyup ${KEY1}; xdotool keyup ${KEY2};` trick I found that `xfsettingsd` was stealing the key-combo

# Workaround #
- I removed all the entries in the settings (I've spent so much time already today that I didn't have time to pinpoint, I don't like spreading my shortcuts all over the place anyway)
- Now, voila, ctrl+f and ctrl+d works as usual.

# My setup #
- Ubuntu 17.04 / Zesty
- `xfce4-about` says version is 4.12

# Possible complexity adders #
- I have quite an elaborate xmodmap I've refined over the years to my liking, shared via git over several machines
- I keep all my shortcuts in xbindkeys, shared via git over several machines
- I do basically all my window-managment via xbindkeys -> xdotools
   - Works (almost well) in Ubuntu Unity, which has been nice to use, but it has it's issues with not having "real" workspaces which fails my setup
   - Works in Gnome Desktop, but I couldn't get a global menu to work there, which I'm used with since the Amiga 500 era
   - Now - with above caveat - works flawlessly with xfce4 - and global menu - so I dub it the winner hands down! Yippie!

# Word of Mouth... #
- Reports I've seen in forums have been even goofier, like plain `e` and `4` not working, etc. variations.
- One person mentioned it starting with 4.12 - with no problems in 4.10 - I just pass this information along here.