Ubuntu 16.04 LTS x86 64-bit.
COLLADA exporter does not emit layer information.
The COLLADA spec for the<node> element defines an attribute "layer". The spec says "layer ListOfNames: The names of the layers to which this node belongs. For example, a value of foreground glowing” indicates that this node belongs to both the layer named foreground and the layer named glowing. The default is empty, indicating that the node doesn’t belong to any layer. Optional".
So the current output,
<node id="Plane" name="Plane" type="NODE">
<node id="Plane" name="Plane" type="NODE" layer="Layer0">
or, for user-named layers (a feature of a standard add-on)
<node id="Plane" name="Plane" type="NODE" layer=Physics">
The "layer" attribute is "Optional", but the description of "Optional" at the beginning of Chapter 2 of the COLLADA spec indicates that if you have the feature in your program, it should show up in COLLADA output. Makes sense, and it's clear how this should work:
(At the beginning of Chapter 2, the COLLADA spec says: Each “Requirements” section details options that must be implemented completely by every compliant tool. One exception to this rule is when the specified information is not available within a particular application. An example is a tool that does not support layers, so it would not be required to export layer information (assuming that the export of such layer information is normally required); however, every tool that did support layers would be required to export them properly.)
(A use case for this is that it would allow solving a painful problem with the Second Life COLLADA importer, which currently requires a separate COLLADA file for visible and physics layers. When multiple files are created by exporting only the selection, they don't always have the same coordinate system, resulting in misalignment.)
Exact steps for others to reproduce the error
Export a file with two layers, preferably named ones, and examine the <node> entries in the COLLADA file.