Don't know if you are using CWP or IWP, but this link may be helpful: PHP API : Longer to load a large field instead of 10 smaller ones...
This is one of many acknowledged bugs that can be found in the Known Bug List here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: http://www.4shared.com/file/8orL8apk/FMP_Bugs.html
I am using CWP with fx.php - How can I check the performance of the web publishing server? Is there a third party app which will help me understand if the web publishing engine is overloaded?