Looks like a bug to me but you don't have to loop through all 256 characters to show that CHR(0) is not supported by TAG property.

o = CREATEOBJECT("custom")
lcStr = ">" + CHR(0) + "<"
o.Tag = lcStr

? LEN(o.Tag), o.Tag == lcStr
* Observed: 1, .F.
* Expected: 3, .T.

>

>* Tag documentation:
>* Expr
>* Specifies any string.
>
>WITH CREATEOBJECT("custom")
>	FOR k=0 TO 255
>		.Tag= 'x'+CHR(m.k)+'x'
>		IF .Tag == 'x'+CHR(m.k)+'x'
>			LOOP
>		ENDIF
>		? M.K,.Tag
>	NEXT
>ENDWITH
>