Copying and pasting results in duplicate output

Created by: a3nm

When I copy text rendered by MathJax (e.g., on CSTheory or on my website) and paste it in a plain text editor, the contents of equation appear twice, e.g., on the first page:

An antichain of a poset (P,<)(P,<) is a subset of pairwise incomparable elements, namely, a subset A⊆PA⊆P such that there are no x,y∈Ax,y∈A with x<yx<y. By a result of Provan and Ball, it is known that it is #P-hard, given a poset, to compute its number of antichains.

I can reproduce this with Firefox and Chromium. It appears that the contents of the MJX_Assistive_MathML elements are copied in addition to the rendered contents.

Is there a way to ensure that copying and pasting MathJax rendered text does not result in this?