HTAdd silently accepts adding the same key again, adds into new slot

[fingolfin]

Example:

gap> SetInfoLevel(InfoOrb, 3);
gap> ht := HTCreate(1, rec(hashlen:=5));
<hash table obj len=5 used=0 colls=0 accs=0 (can grow)>
gap> ht := HTCreate(1, rec(hashlen:=3));
<hash table obj len=3 used=0 colls=0 accs=0 (can grow)>
gap> HTAdd(ht,1,1);; HTValue(ht, 1);
1
gap> HTAdd(ht,1,2);; HTValue(ht, 1);
1
gap> HTAdd(ht,1,3);; HTValue(ht, 1);
1
gap> HTAdd(ht,1,4);; HTValue(ht, 1);
#I  Hash table too full, growing...
#I  Growing hash table to length 11 !!!
#I  Done.
2

Expected behaviour: I would expect HTAdd to report an error; or at least warning, and then drop the new value. Alternatively, it could also update (which then render HTUpdate obsolete)