Matlab 2012a subs() BUG?

I have function that is a sum of multiple sinusoidal functions. It is x(t).

I try to first do time shift, no problem:

syms x;
syms t;
%define x, some long sinusoidal function
r1 = subs(x,t,t-1)

Everything up to here runs fine. Next I want to evaluate the shifted function.

subs(r1, t, 0)

Now after this step above the result is NaN Result should be 1, by plotting...

[Walter Roberson]

Please show r1

NaN could show up if the expression is singular at t=0

[ha9981]

NaN shows up for r1 and r2 when evaluating at any integer value! Figure below.

[Walter Roberson]

Okay, but you have not indicated what r1 or r2 are