I don't know if there are more to this or if it would break some other rules but as of my testing it should be fine to remove this rule for headers that have no sorting applied to them.
This is the case already for "normal sized" tables as the padding-right rule is only applied if there is a sorting class to the element. But it has been forgotten for the table-sm variant. So there are two options that I can see.
Specify this rule does not apply if there is a sorting_disabled class
Do the same as what was done for the normal sized table in the following commit: 4e611f31ff
On line 605, column.sTitle is set to the TH's innerHTML.
On line 1816, column.sTitle is compared with cell.html().
If you have child elements with event handlers on them inside the TH, these are not the same in IE8 (see https://gist.github.com/simonbrent/933e552739477f4be3ab#file-test-html)
As a result, the check on 1816 fails, the contents of the cell is replaced, and the event handlers are removed.
Comparing instead with cell[0].innerHTML fixes this issue.
