The strel class was implemented in the @class style (this was before Octave had classdef).  In order to support dot notation, we overload subsref.  I am thinking the problem is there, and our poor support for strel arrays.  Maybe we need to overload subsasgn or one of the other subsX methods.

But we should probably be moving strel to classdef instead, which is meant to handle those issues for us.

Here is how to reproduce the behavior:

clear
pkg load image

se = strel ("square", 1);
vec(1)=se;
vec(2)=se;

As a result I get an infinite stream of error messages like this:

[...]
error: parse error
error: called from
    print_usage at line 91 column 5
    size at line 31 column 3
error: Invalid call to isempty. Correct usage is:

-- isempty (A)
error: parse error
[...and so on...]

This happens with Octave 4.2.1 and image-2.6.1 (both current releases). I have seen this under Linux (Ubuntu 16.04) as well as under Windows (7).

I am not sure if this is a bug in the definition of the strel (class) object (this would be part of the image package). Or if this in a bug in core Octave. But even if there is something ill-defined with the (image package) strel object, I think core Octave should just throw one error message and then stop. The current behavior of starting an infinite loop of error messages cannot be right on the (core) Octave side. This loop of error messages can NOT even be stopped by hitting Ctrl-C.