I followed this up with Mathworks support and recieved this response. Hopefully you will find it helpful
Please note that the source of a warning with the structure
"Warning: A value of class "<some class>" was indexed with no subscripts specified. Currently the result of this operation is the indexed value itself, but in a future release, it will be an error."
is code which uses indexing into variables with empty parentheses. When all warnings are enabled, indexing into variables with empty parentheses issues a warning message of this type. For example, the following code issues a similar warning as listed below
>> x = [1 2 3 4 5];
>> y = x()
Warning: A value of class "double" was indexed with no subscripts specified. Currently the result of this operation is the indexed value itself, but in a future release, it will be an error.
1 2 3 4 5
Note that this warning message is suppressed (i.e. 'off') by default. To see a list of warnings suppressed by default, enter 'warning' command without arguments in the MATLAB Command Window after restarting MATLAB. The command "warning('on')" turns on all warnings, including those which are 'off' by default. If you want to enable all other warnings except this particular one, I would recommend you to execute the following commands in the MATLAB Command Prompt:
I hope the above information is useful to you. If there is any further query regarding this, please feel free to reply to this mail and I will be happy to assist you further.