I've got a client running a highly-customized Zen Cart v1.5.1 that recently transferred to bluehost (yes, I know ...) on PHP 5.4.43 and just ran into the weirdest thing:

I go to one of the configuration screens and change the first value in the list. Upon clicking the "Update" button, I'm returned to the overall configuration display ... but the value hasn't been changed. I can click the next item in the configuration screen and, like magic, the change I made to the first item now displays! This is using the built-in configuration handling in the Zen Cart admin.

I've checked the configure.php files to ensure that all the file-paths are proper (they are) and the Configuration->Sessions to make sure that the session-save-directory is the /cache folder (it is).

There are other bits of funkiness going on on this site after the move, but I believe that the above issue is a large, underlying factor.

I'd appreciate any/all clues or other pieces of information to hunt up.