I performed the latest update on my EVO 3D (version 2.3.4) and after this update I haven't been able to use my KEYBOARD right. it shows for a couple of times when I'm writing doesnt matter where (texting, emailing, on whatzapp, convo, etc..) it stops working and the keyboard doesn't show anymore even when I try to summon it again.
The only way it comes back is to close the application I'm using and go to the same process you read up.
1) Power your phone off. PULL the battery out of the phone for 30 seconds. Place it back into the phone and power it on. Sounds funny but this fixes many many strange issues.
2) Go Menu > Settings > Applications > Manage Applications > All > Your Keyboard (Touch Input for stock) > Force Stop then click on Clear Data
3) Go Menu > Settings > Language & keyboard > Touch Input > Text input > Reset Calibration (Resets to defaults) Or you can do Calibration tool (To set up manually)
4) If all of that fails Install a new keyboard and see if it suffers from the same issue.
5) Hard reset the OS!
I am sure others will have more ideas. Hell mine may not even help at all. This is what I have figured out in my VERY limited keyboard issues. I still use the stock keyboard. I have had my disappear on me in the past. But only in the stock messaging app so far. I think its an HTC bug! Yours may not even be related. Just a thought!
Hope this helps you out! Good luck with the keyboard!