After upgrading to 1.3.6, I began noticing that grouped windows would steal the focus. For example I have FireFox windows grouped together. When I selected the first window in the group and tried to open a new browser tab (ctrl^T), it would open the tab in the second FireFox window. A few times I also noticed keyboard input showing up in unfocused terminal windows (also grouped), even though I was typing directly into the address bar of FireFox. I found that restarting FluxBox corrected the issue. Any feedback would help greatly.
OS: Linux
Distro: Fedora 22
FluxBox Config: https://github.com/postmodern/dotfiles/tree/master/.fluxbox
Is that behavior limited to firefox or did you encounter it with any other client as well (thunderbird doesn't count ;-)