Really weird eclipse keyboard behavior/bug?
If you see the same symptoms on Eclipse Windows, just press all your mouse buttons (including the wheel if you have one) at the same time together, and that seems to fix it.
Same weird problem, this worked for me: I just figured out that if I switch editor and then back again, backspace starts working again. (source)
I was able to "restore" arrow and backspace keys by "Refreshing" the project.
UPDATE: 7/11/2017 I've not had this problem reoccur in a couple of years now. Either Eclipse fixed the problems or a more recent version of Mac OSX has fixed something. For the record I'm running Eclipse 4.5.2 on OSX 10.11.6.
UPDATE: 4/29/2011 Now it looks like this is not a Workspace or keyboard preferences issue at all. This just happened again but restoring from older Workspaces did not fix the issue. I finally had to reboot my Mac which seemed to resolve things. I'm going to try a restart in the future immediately if I see this again. I've submitted this bug with Eclipse. Please add a "me too" comment to the bug if it has not been fixed and you can reproduce this on your system.
I also have heard that on Macs, you can solve this by getting the unit to sleep either by closing the laptop lid or pulling the Apple menu down to sleep, wait a few seconds, and then starting it again. I've not tried this yet.
BTW, when this happens refreshing and other mechanisms have not worked.
UPDATE: 4/13/2011 Although the below instructions did fix my keyboard issues, I discovered other problems with my configuration and was finally forced to recover my Workspace from backups.
NOTE: This is not recommended but is here for information purposes. Typically these keys are handled by the native widget and are not defined.
So I just had the same problem under Eclipse 3.6.2.r362 on Mac OSX 10.6.7. Delete to the left and arrows not working. They worked in other applications. Option-Arrows worked fine to move a selection around. Arrows worked in the keyboard preferences window. Switching to another application and back didn't work. Restarting eclipse made no difference. Switching keyboard schemes from Emacs -> Default -> Emacs didn't work. Pressing all of the modifier keys did nothing. I tried all of the following and nothing works: Rebuilding the project, refreshing the source, restarting Eclipse.
Finally, I was able to fix this by going to the Preferences -> General -> Keys and resetting each of the bindings for the following keys. The bindings for each of the keys were blank.
Delete Previous
to backspaceLine Up
to up arrowLine Down
to down arrowPrevious Column
to left arrowNext Column
to right arrow
This worked but then I noticed that all of the emacs key bindings were screwed. I thought they worked before so I'm not sure when this happened. I had to restore default key bindings (after writing down the ones that I had customized) and then restore my customized settings.
Makes me wonder what other key bindings have been reset and what did it. Frustrating but at least I can get back to coding.