Why does the function ISA return different values on different platforms?

On WINDOWS machine:

sys = rss(3,1,2)

isa(sys,'LTI') %answer is 1

isa(sys,'lti')  %answer is 1

On Unix/Mac:

sys = rss(3,1,2)

isa(sys,'LTI') %answer is 0

isa(sys,'lti')  %answer is 1

Answer 1

[MathWorks Support Team]

The ability for the ISA function to recognize upper case strings on Unix is not available in MATLAB 7.3 (R2006b).

To work around this issue, please use lower case letters as the class name input to ISA.