Your trace indicates a gtk2 immodule loaded by gtk3, causing crashes as gtk2 symbols will conflict with gtk3 symbols. How did you enable uim on your system?

I enable it by running uim-toolbar-gtk-systray on both systems. Besides that, I followed the instructions as outlined by the uim wiki entry.

Hum, first of all, I cannot reproduce this issue, so something is probably misconfigured on your computer.

Running uim-toolbar-gtk-systray does not enable uim; I assume you actually enabled it by setting the GTK_IM_MODULE, QT_IM_MODULE, and XMODIFIERS variables in your .xinitrc before running uim-xim, just as explained here: https://wiki.archlinux.org/index.php/Input_Japanese_using_UIM#Environment_variables . Can you confirm this and check that the lines are exactly as in your .xinitrc?

Also, could you:
- restart X and see if it solves your problem; and, if not,
- remove just the GTK_IM_MODULE line from your .xinitrc, restart X, and see if it solves your problem.

Sorry, I misunderstood the question originally being asked. I start wmfs using the console display manager and a script (not .xinitrc), and the lines read:
export GTK_IM_MODULE="uim"
export QT_IM_MODULE="uim"
uim-toolbar-gtk-systray &
uim-xim &
export XMODIFIERS=@im=uim

I also remember having to manually force the creation of a immodule file on my PC before the update. Removing the GTK_IM_MODULE line results in no change whatsoever.

Could you be more specific about that creation of immodule file?
Could you also tell us what your architecture is, and put the output of `ls -l /usr/lib/gtk-*/*/immodules/` in a pastebin and post the link here?

I'm not entirely sure what I did anymore because it was a while back, but I believe I was forced to add a line manually to gtk.immodules in order to get uim working (followed instructions in a bug report I believe), but this should have been done automatically by the package, since it's present on my laptop too.

Architecture: x86_64
Pastebin link: http://pastebin.com/xrXAj5px

Well, your two computers behave differently, so one must be configured differently from the other.
And since we cannot reproduce your issue, you have to find what you manually did.

I've been looking around and the only possible change I made was copying the line about uim from my laptop over to my PC from the /etc/gtkrc-2.0/gtk.immodules file, since it wasn't added when uim was installed. Regardless, I will see if I can migrate my settings over from my laptop again tomorrow (it's 11pm here).

After setting GTK_IM_MODULE to "xim" instead of "uim" it's working on my PC as well. However, the configuration for my laptop was exactly the same (laptop was setting the variable to "uim"). Either way, it's working and I have run out of things to check, so I'd say this can be closed.

Very well.