The only possible cause that I know of would be invalid XHTML - I just validated the default style (except the Moderator Control Panel and User Control Panel, those would take me the best part of a weekend), and the validation issues that I found were minor issues that couldn't have caused your problem.
The issues that I found were:
- On viewtopic.php and faq.php, the "Go to top" image was missing its ALT attribute.
- The search image button in the header was using a deprecated attribute.
- Some invalid markup (a <div> tag within a <span> tag) on the memberlist.
Of course, I fixed all of those.
I still maintain that this is a browser/phone bug, and NOT an issue with the forum itself.
Kia kaha, Kia māia, Kia manawanui.