This enhancement has been incorporated in Release 2008b (R2008b). For previous product releases, read below for any possible workarounds:
The main difference between mux signals and bus signals is that the components of a bus signal can include more than one data type and can be hierarchical, while the components of a mux signal must all have the same data type and cannot be hierarchical. The documentation of Composite Signals explains this distinction:
<http://www.mathworks.com/help/releases/R2012b/simulink/composite-signals.html>
Buses can provide consistency checking with the use of a Bus Object, but muxes cannot. Please refer the following for more information:
<http://www.mathworks.com/help/releases/R2012b/simulink/ug/using-bus-objects.html>
Buses can be realized as structures in generated code, but muxes cannot. See:
<http://www.mathworks.com/help/releases/R2012b/simulink/slref/buscreator.html>
MathWorks strongly discourages mixing muxes and buses. For example, do not use Mux blocks as Bus Creators. See:
<http://www.mathworks.com/help/releases/R2013a/simulink/ug/avoiding-mux-bus-mixtures.html>
The Demux block has a Bus Selector mode. For information about when to use this mode, see:
<http://www.mathworks.com/help/releases/R2012b/simulink/slref/demux.html>
Using a Bus Selector block, you can change the order of signals. This cannot be done with a Demux block. An example is attached to this solution (bus_mux_vec.mdl). In bus_mux_vec.mdl model, the order of the two input signals going through the Bus Creator and the Bus Selector blocks has been changed. After running the model, you will see [1 2 3 4] in Scope1, not [5 6 7 8]. However, the order of the two input signals going through the Mux and Demux blocks cannot be changed, so you will always see [5 6 7 8] in Scope1. For more information on how to change the order of signals using a Bus Selector block, see:
<http://www.mathworks.com/help/releases/R2012b/simulink/slref/busselector.html>
Although the Demux block cannot rearrange the order of muxed signals, the Signal Selector block can. See:
<http://www.mathworks.com/help/releases/R2012b/simulink/slref/selector.html>
Bus signals that are hierarchical or include components of different data types can drive only Bus Capable blocks. See:
<http://www.mathworks.com/help/releases/R2012b/simulink/ug/bus-capable-blocks.html>
This limitation does not apply to a mux signal as long as the Mux block inputs are vectors or vector-like. A vector-like signal is any signal that is a scalar (one-element vector), a vector, or a single-column or single-row matrix. For example, a muxed signal can drive a Gain block, while a bus cannot. See:
<http://www.mathworks.com/help/releases/R2012b/simulink/slref/mux.html>
For a list of Simulink virtual and conditionally virtual buses, see:
<http://www.mathworks.com/help/releases/R2012b/simulink/ug/virtual-and-nonvirtual-buses.html>
The Bus Selector block supports matrix inputs. The Demux block does not support matrix inputs unless you double click on the Demux block and check "Bus selection mode". Run the attached model, bus_mux_matrix.mdl. It should work correctly. However, if you double click on the Demux block, uncheck "Bus selection mode" and run the model, it will generate an error.
The Bus Selector block has an option labeled 'muxed output'. This option is mislabeled: the output is a Bus and should be treated as such. Refer to the Related Solution for more information on this feature.
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