Here is a bug many over at XDA are confirming (myself included) on builds JRO03C, JRO03H, and JRO03L (also began happening since 4.0.4 apparently as well). How to reliably produce it (I know this happens on maguro at least):

1. Open Messaging
2. Tap on Home icon
3. Tap on Recents icon
4. Tap on Messaging in the Recents list
5. Try typing

You will often find that if you type fast and/or even with medium pressure, half the keypresses won't register. This happens with every keyboard I've tried and is screen-wide (usually takes two tries just to press the home button after you switch back to Messaging). It's definitely a software issue because locking and unlocking the screen makes the bug go away. If you've seen this, star it here:

Issue 29734 - android - 4.0.4 touchscreen sensitivity irregularity - Android - An Open Handset Alliance Project - Google Project Hosting

This effectively makes the Recent Apps feature of Android completely and utterly useless.

I apologize if this has already been posted somewhere on this forum. I couldn't find it through searching anywhere.