I have tested the described scenario locally with Telerik UI for ASP.NET AJAX version 2013.2.717.40 and .NET v4.0
. Unfortunately, I could not reproduce your issue, neither on iOS 6.1.3 Safari and iOS 7 Safari, nor on Mac OSX Safari 7.
In all cases I achieved well structured RadToolBar with RadToolBarSplitButtons as the ones that could be seen on the Item Types RadToolBar online demo
. The online demo is running with UI for ASP.NET AJAX version 2014.1.403.40.
I would suggest that you try to isolate the code that causes the issue by removing bits of code, external css, changing width property values and checking if the issue persists after each change.
Another option is to check if upgrading the UI for ASP.NET AJAX version would fix the issue - you may use trial dlls for a quick check.
If you need additional assistance to overcome the issue, in order to assist you in the most efficient way I would kindly suggest that you provide us with a very simplified runnable project (aspx, code behind and CSS) that demonstrates the behavior that you describe. Thus, we could test it locally and determine what might be causing the issue that you are experiencing.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.