Google has expanded its legal agreement with developers working on Android applications to specifically prohibit them from taking any action that could lead to a fragmentation of the operating system.

The prohibition was added to the terms and conditions for Google's Android SDK (software development kit), which developers must accept before using the software to build Android apps.

The previous version of the terms of service, published in April 2009, didn't address the issue, but the new terms published on Tuesday include this new paragraph:

"You agree that you will not take any actions that may cause or result in the fragmentation of Android, including but not limited to distributing, participating in the creation of, or promoting in any way a software development kit derived from the SDK."

Google did not respond to several requests for comment.

The issue of Android fragmentation has been gaining increased attention, but it's happened largely as a result of actions taken by Google and Android handset makers, not developers. It's a problem because it means that Android applications may not run properly across all Android devices.

"It continues to be a problem, both on smartphones and tablets," said Avi Greengart, research director at Consumer Devices. "Google has talked about multiple initiatives for dealing with it, but none of them have successfully addressed it."

He cited as an example this week's launch of Android version 4.2, also known as Jelly Bean. Despite a high-profile launch on several new Google-branded devices, handsets and tablets from competitors are still without the new operating system.

"HTC is rolling out the Droid DNA, which has an extraordinary specification list, but they can't claim they have the latest and greatest operating system," Greengart said.

"[Google] perpetually puts Android licensees behind the curve," he said. "The software features that Google puts into the latest versions of its OS are often not available for consumers or for developers to exploit."

That's a big contrast to Apple, which rolls out updates to phones at the same time and often continues to provide support and new features for at least a year after the phone has been bought.

Martyn Williams covers mobile telecoms, Silicon Valley and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is martyn_williams@idg.com