Page error changes CSS.

I'm not sure if this is a sky issue or general drupal. If a user fails to provide a value to a required field (for example), clicks save, the page looses all custom css when it's regenerated with the error/notice. And it seems to only happen with the image field. For example: if i edit my profile and remove all the images, then save, drupal reports with notice that the field needs a picture (expected behavior), but it also displays the page without my custom css.

I can see in firebug what file is changing when I do a comparison.

<link href="http://www.site.com/sites/default/files/css/css_xE-rWrJf-fncB6ztZfd2swhuxqgxu4WO-qwma6Xer30m4.css" rel="stylesheet" type="text/css" media="all">

Note:
Performance settings for cache lifetime and expiration is "none".
I have enabled Aggregate and compress CSS files.
I believe all my other related theme settings are still at default.

Any ideas what could be causing this.

SL