Why have option- shortcuts in text fields started inserting special characters? I'm a daily user of a couple of IntelliJ IDEs. Unusually for Mac apps (probably because they're Java, not real native apps) they make liberal use of option/alt- keyboards shortcuts. I probably use these unthinkingly hundreds of times a day.

Suddenly they're not working. Either they do nothing, or if the cursor is in a text field, they insert a special character (eg. Ø for option-shift-o).

I don't think this has anything to do with the IntelliJ software per se. I mention them for completeness (and because I didn't use the option-key shortcuts in other apps, so can't be sure of the behaviour elsewhere). This is on a 2013 MB Pro, with both the internal and a bluetooth keyboard.

The one wrinkle in setting up my question is that it's possible this started when I installed the 10.11 RC (I had previously been on release Yosemite). I'm not quite sure, unfortunately, as in the heat of getting work done, I ignored the new shortcut behaviour when it first cropped up (so don't quite remember when that was).

So, has 10.11 introduced something that might have caused this different behaviour? Or is there a setting I might have unwittingly changed? I'd be grateful for any suggestions as to why these shortcuts could have changed behaviour overnight, and what I can do to get the old behaviour back.
Using option (alt) key is the default way to enter non-latin characters from a keyboard which layout does not have these characters. For instance: I'm Polish, so I need to use Polish characters (like 'ą', 'ę', 'ó' etc.). To do that I use option key (option+a, option+e, option+o). 

You can see the variants of keys of your keyboard by enabling keyboard preview: go to System Preferences, choose Keyboard and check the check box in the bottom called 'Show Keyboard &amp; Character Viewers in menu bar' (http://osxdaily.com/2013/06/21/mac-virtual-keyboard-os-x/). Enable it by opening the keyboard menu ('Show keyboard viewer', you can find the instructions under the same link). Now hold the option key - you'll see the variants of keys in your keyboard - you should see the reason to type 'Ø' when you use option+shift+o.

EDIT:

The answer I wrote was the answer to the question in the title: "Why have option- shortcuts in text fields started inserting special characters?".

There a few options: 


if you could do that in previous version of OS X then the new version may have changed some settings (see: https://developer.apple.com/library/mac/documentation/UserExperience/Conceptual/OSXHIGuidelines/Keyboard.html - they can choose to change keyboard behavior as they want and they mention it). 
Also, since entering the text is system-based functionality it may
not be overriden by default - you need an external tweaking software
to do that. 
It may also be a bug - you're using an unstable version
of the system.


You may find a solution (the tweaking software I mentioned) to your problem in answer of this question:
https://stackoverflow.com/questions/11876485/how-to-disable-typing-special-characters-when-pressing-option-key-in-mac-os-x