The new touchscreen-friendly user-interface system promised for next desktop version of Ubuntu has been PULLED just weeks before its release.

Mir and XMir – the Linux distro's replacement for the age-old X Windows graphics stack – will now NOT be enabled by default in the 13.10 desktop build - due out on 17 October.

Mir is the new display server that will, according to Ubuntu-maker Canonical, “unlock next-generation user experiences for devices ranging from Linux desktops to mobile devices powered by Ubuntu”. XMir is a halfway house, being an X Windows compatibility layer for users who can't run a pure Mir stack.

The plan to is eventually replace X Windows in Ubuntu with Mir so that software can seamlessly run across all supported devices - from tablets and phones to laptops and desktop computers. Version 13.10 was supposed to use Mir/XMir by default on the desktop or fall back to plain-old X Windows if forced to by a graphics driver incompatibility.

But last night Um Bongo developers said they had decided to drop the new software from the default configuration because there are “outstanding quality issues”.

Penguinistas with handheld gadgets can still use Mir in the Ubuntu Touch 13.10 release. And brave desktop users can, of course, rummage around in their system and override 13.10's settings to enable Mir/XMir.

Canonical’s head of product strategy engineering Oliver Reis denied Mir had failed, but he could not give a date for when the code will be switched on by default. The next available opportunity is Ubuntu 14.04, due out in April.

“Mir has made significant progress,” he noted in an FAQ about the decision. “The only change is that we needed a little more time.”

Reis wrote in an email yesterday evening that technical problems stalled the planned Mir rollout:

Many of these issues live in the XMir part of the stack, which provides the integration between the X server and the underlying Mir system compositor. More specifically, the multi-monitor support in XMir is working, but not to the extend we'd like to see it for all of our users. The core of Mir is working reliable, but with XMir being a key component for our 13.10 goals, we didn’t want to compromise overall Ubuntu quality by shipping it.

The decision to switch off Mir in the default settings comes after Intel pulled support for XMir from its graphics drivers. The chip giant, which backs the rival display engine Wayland, gave little reason for the snub. The engineer who kicked Canonical's XMir code out of the xf86-video-intel driver simply said: “We do not condone or support Canonical in the course of action they have chosen, and will not carry XMir patches upstream.”

That's a slight pain in the backside for Canonical's programmers, who will have to maintain their own unofficial, XMir-supporting version of the xf86-video-intel driver, rather than rely on Intel to maintain support for the compatibility layer.

Ries denied the chip giant triggered the decision to drop Mir/XMir as a default from 13.10.

“The decision was made by our engineering management team and was based solely on the current quality feature set we defined for XMir, independent of any discussions with Intel," he said.

Intel has invested time and effort in Wayland, which was designed in 2008 by Linux kernel engineer Kristian Høgsberg who is now a software engineer at Intel. Canonical, though, rejected Wayland, claiming it was too inflexible and couldn't handle stuff like 3D gestures, and instead plumped for its own protocol: Mir. ®