html:
It sounds like your javascript is breaking the native IE10 placeholder functionality.
To test this, and hopefully fix it, wrap the javascript you have written for placeholders in a conditional statement, so that it only applies to IE9 and below.
Alternatively, there is a very nice jquery plugin by Mathias Bynens that is available for free and handles all of this for you: https://github.com/mathiasbynens/jquery-placeholder
Some CMSs already have a plugin built using this code. The Wordpress plugin is here: http://wordpress.org/plugins/html5-placeholder-polyfill/