I noticed that that is different from the setting in your other database ... it may or may not have any affect on things ...

Also, in your configure.php files, you are using:
Code:
define('SQL_CACHE_METHOD', 'file');
You might try:
Code:
define('SQL_CACHE_METHOD', 'database');
To see if things work better on your other database ...

When setup for your other database, did you check the setting, as DrByte suggested for:
Admin->Configuration->Shopping Cart->Product Quantity Decimals
Or check this directory as he asked?
Are there any files in your /includes/init_includes/overrides folder? If so, what exactly are they there for? Are any files missing from (or damaged in) the /includes/init_includes folder itself?