Had the flashing button, super slow unusable edit page issue - the answer for me at least seems to be that I had missed updating the settings file in the root directory when manually upgrading from 2.5 to 2.51 - specifically the newest wp-settings.php file (4/21/08) includes the following on line 335 that is missing in earlier versions
the newest files include this code at lines 335-342
* It is possible to define this in wp-config.php
* @since 2.5.0
if ( !defined( 'AUTOSAVE_INTERVAL' ) )
define( 'AUTOSAVE_INTERVAL', 60 );
Comparing files from the broken blog with a new install on both the same host and another hosting company that doesn't use fantastico but offers one click install it became apparent that the files were different, so even if you replaced it as part of your upgrade getting the newest version from a 2.5.1 download post april may be the answer.
Before this I also tried the following to fix this issue with no success:
- Deleted the files in wp-content/uploads/js_cache
- Set the WPLANG define in wp-config.php to 'en'
- Cleared all the caches on browser
- Updated Tiny MCE using the following
√1. Download the latest version of TinyMCE from the offical site:
√2. Unzip the following files into wp-includes/js/tinymce:
√3. Delete the files in wp-content/uploads/js_cache. √Clear all the caches on browser, √manually reload this URL on your blog: /wp-includes/js/tinymce/tiny_mce_config.php to verify
Also removed all dev and live blog cookies before restarting browser
Again removed new files from wp-content/uploads/js_cache
Downloaded and installed tinymce-advanced plug in - turned it on, repeated all cache clearing, turned it off cleared caches etc. no love
So reading this post at http://trac.wordpress.org/ticket/6844 led me to suspect that my upgrade had not been as thorough as i thought it had. Like in this post my browsers were telling me they were stuck in a continual loop looking for admin-ajax.php and the new settings file with the interval definition in it seems to have ended that issue which allows for speedy typing and easy posting.
I am still waiting to hear whether any other authors on this blog are still having issues but i think this is the fix and hope it helps someone.