HTML5 with MathML has problem with numerical attrubute values

I MAY have found a bug.

The validator at "http://validator.w3.org" does not like numerical
attribute values.

For example when validating:
https://www.eyeasme.com/Joe/MathML/HTML5_MathML_browser_test.html

Many attribute values are marked as "Bad value"

The easiest ones to check are those attributes which can only be
positive integers, for example "rowspan" and "columnspan".

The validator complains about the line:
<mtd columnspan="2">

with the message:

Error: Bad value 2 for attribute columnspan on element mtd.
>From line 1273, column 21; to line 1273, column 40
<mtd columnspan="2">↩

I checked the latest recommended MathML spec at:
http://www.w3.org/TR/MathML2/chapter3.html#presm.mtd
Section 3.5.4.2 Attributes

and the latest MathML next generation spec at:
http://www.w3.org/TR/2009/CR-MathML3-20091215/chapter3.html#presm.mtd
Section 3.5.4.2 Attributes

Both specify that the attributes "rowspan" and "columnspan" have
positive integer values.

Is this a bug or am I missing something?

Joe