A cell containing “10 oz.” will be treated as alpha, not as numeric. Try harder to DWIM numericness in a cell.
This is low-priority because you can work around it with custom sortkeys if required, by doing something like this:
<table class=“sortable”>
<thead>
<tr><th>Item</th> <th>Weight</th></tr>
</thead>
<tbody>
<tr><td>Bag of sugar</td> <td sorttable_customkey=“10”>10 oz.</td></tr>
...
</tbody>
</table>