they were meticulous in what they were doing, how can it be a "bug"?

I keep hitting behaviour that is very weird.
Having compiled the following program into an executable

#include <stdio.h>
#include <stdlib.h>
#include <gsl/gsl_spmatrix.h>
#include <gsl/gsl_version.h>

int main(int argc, char * argv[]) {
 long t, initial_value,left_shift, addon;
 initial_value = strtol(argv[1], NULL, 10);
 left_shift    = strtol(argv[2], NULL, 10);
 addon         = strtol(argv[3], NULL, 10);
 size_t v = (size_t)initial_value;
 v <<= (size_t)left_shift;
 v += (size_t)addon;
 printf("gsl header version : %s\n", GSL_VERSION);
 printf("gsl library version: %s\n", gsl_version);
 printf("size of _size_t is %d bytes\n", sizeof(size_t));
 printf("initial value: %d\nleft shift: %d\naddon: %d\n", initial_valu
+e, left_shift, addon);

 gsl_spmatrix *m = gsl_spmatrix_alloc(v,v);
 printf("size1: %lu\nsize2: %lu\nnz: %lu\n", m->size1, m->size2, m->nz
+);

 return 0;
}
[download]

I then execute it 4 times with different input arguments:

D:\C>gsl_spm.exe 1 16 28000
gsl header version : 2.7.1
gsl library version: 2.7.1
size of _size_t is 8 bytes
initial value: 1
left shift: 16
addon: 28000
size1: 93536
size2: 93536
nz: 0

D:\C>gsl_spm.exe 1 16 28001
gsl header version : 2.7.1
gsl library version: 2.7.1
size of _size_t is 8 bytes
initial value: 1
left shift: 16
addon: 28001
size1: 93537
size2: 93537
nz: 0

D:\C>gsl_spm.exe 1 16 28002
gsl header version : 2.7.1
gsl library version: 2.7.1
size of _size_t is 8 bytes
initial value: 1
left shift: 16
addon: 28002
size1: 93538
size2: 93538
nz: 0

D:\C>gsl_spm.exe 1 16 29002
gsl header version : 2.7.1
gsl library version: 2.7.1
size of _size_t is 8 bytes
initial value: 1
left shift: 16
addon: 29002
gsl: init_source.c:144: ERROR: failed to allocate space for data
Default GSL error handler invoked.
[download]

The first three runs seem quite sane to me, but I don't see a good reason that the 4th run should blow up like that just because the third command line argument has been raised by 1000.
Maybe it's optimization at the expense of correctness ?
Or maybe there are some mysterious rules of usage that I am overlooking. (I don't normally use the GSL library at all.)
I get the same results with gsl-2.6.1.

Cheers,
Rob

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