plot legend shows wrong linespec

Starting with no open figures, and some data already computed, I made a plot as follows:

load('data')  % I did not use this commands initially.  It is here for demonstration.
figure
plot(t,molTot,'-rx',t,molGas,'-bo');
legend('a','b')

and I got a plot like the plot above, including the incorrect lines in the legend.

I had previously seen this problem in multi-panel plots made by a complicated script. I looked in the figure properties and saw nothing obvious, but I'm not a figure property expert, so I don't know exactly what to look for. Therefore I closed all open figures, before issuing the three commands above (without the 'load(...)') - to see if the bad legend occurred with a new and simpler figure. And it did. I closed the figure shown above, then repeated the three commands above, with the same result. Therefore I saved variables t, molTot, molGas in file data.mat. Then I closed and restarted Matlab. I did

load('data')
figure
plot(t,molTot,'-rx',t,molGas,'-bo');
legend('a','b')

and I got asnother figure with an incorrect linespec in the legend, as seen above.

Why is this happening? [Matlab 2023b on Windows 11 Pro.]

Thanks.

Answer 1

[VBBV]

d = load('data.mat')

d = struct with fields:
    molGas: [401x1 double]
    molTot: 3.6118
         t: [401x1 double]

%figure
plot(d.t,repmat(d.molTot,length(d.t),1),'-rx',d.t,d.molGas,'-bo');
legend('a','b')

[VBBV]

molTot is scalar quantity while others are not

[William Rose]

Thank you @VBBV and @the cyclist.

Answer 2

[the cyclist]

The syntax you are using created a plot with 402 "lines". The first 401 are red, and the last one is blue.

load('data')  % I did not use this commands initially.  It is here for demonstration.
figure
h = plot(t,molTot,'-rx',t,molGas,'-bo');
legend('a','b')

size(h)

ans = 1x2

402 1

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You presumably intended something more like

figure
h = plot(t,molTot*ones(size(t)),'-rx',t,molGas,'-bo');
legend('a','b')

[William Rose]

Thank you.