Question: Bug in MapleTA?

When I execute the following code in Maplesoft on my computer, there are no problems.  However when I execute the same code in mapleTA occasionally Maple only finds a single input value corresponding with h_given.  Anybody have any idea what is going on?

Basically I have a function, f,  that I am only interested in plotting and analyzing real-valued inputs, t, from =0 to 100 (or so).  At some point I assign an output value, h_given, and I wish to find the correlated real-valued inputs.  From the graph you can clearly see that there are 2 inputs, however the script occassionally only produces 1 output. (when running on mapleTA).

Thanks in advance,

a := MapleTA:-Builtin:-range(1800, 2300, 100):
b := (1/10)*MapleTA:-Builtin:-range(4, 8, 1):
timeT := MapleTA:-Builtin:-range(70, 100, 10):
f := -t*(b*t-b*timeT)^2*(cos(.15*t+4)^2-3)/a:
maxs := NLPSolve(f, t = 0 .. timeT, maximize):
maxim := maxs[1]:
graph := plot(f, t = 0 .. timeT, gridlines = true, 0 .. maxim+10, labels = [t, h(t)], labeldirections = [horizontal, vertical]);
h_given := 10;
expr := h_given-f:
answer_t := Student:-Calculus1:-Roots(expr, t = 0 .. timeT+5);
evalf(answer_t, 2);

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