I'm not sure if it's a new issue or related, but the real problem is as follows. Consider the following xml:

<?xml version="1.0" encoding="UTF-8"?>
<mule xmlns="http://www.mulesource.org/schema/mule/core/2.0"
xmlns:management="http://www.mulesource.org/schema/mule/management/2.0"
xmlns:spring="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://www.mulesource.org/schema/mule/core/2.0 http://www.mulesource.org/schema/mule/core/2.0/mule.xsd
http://www.mulesource.org/schema/mule/management/2.0 http://www.mulesource.org/schema/mule/management/2.0/mule-management.xsd
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd">

<--
However, auto-completion for element names doesn't work.
-->
<!<management:>

</mule>

Check the comments for 2 scenarios. This is a demo with substitution groups in XML schemas, which are valid schemas btw. E.g. other commercial xml-dedicated editors like Oxygen XML work perfectly with them and provide auto-completion.

Issue was resolved