Confirmed.  Re-titling the bug report to be more precise about the issue.

Sample code

figure
plot (1:10, [1:9, NaN])
axis tight

The explanation is rather simple.  When Octave calculates limits for "axis tight" it looks at each axis individually.  In the sample code, the x-data has a minimum of 1 and a maximum of 10 so that is what Octave sets the axis limits to.  Apparently Matlab also checks whether the corresponding y-value is finite.  I tried two variations in Matlab and the limit is 9 in each case.

plot (1:10, [1:9, NaN])
plot (1:10, [1:9, Inf])

But, things aren't always straightforward even in Matlab.  This code produces a line at 45 degrees from 1:9.  There are no line segments after x == 9, and yet the limits of the plot are set at 1 and 11.

figure
plot (1:11, [1:9, NaN, 9])
axis tight

I know why it does that, but it still seems odd since there is no visual data past 9.

Marking as a low priority since there are easy workarounds such as calling xlim or axis with limits that look good to the programmer.