Aah, yes, I forgot about these hex thingies which are convertible to INT. One of these strange days, I get following results

SELECT ISNUMERIC(0X0e) AS E, ISNUMERIC(0X0f)  AS F

E           F          

----------- -----------

0           0

(1 row(s) affected)

while

SELECT CAST(0X0e AS INT) AS E, CAST(0X0f AS INT) AS F

E           F          

----------- -----------

14          15

(1 row(s) affected)

works.