Changing a span's attribute duplicates the whole span

Question

Imagine the user selects some formatted text in edit mode and invokes my plug-in. The selected text corresponds to the following markup:

<span class="foo">hello</span>

Accordingly, this is the markup my plug-in receives as the content string. Now, all my plug-in does is change the class attribute's value. Accordingly, this is the new value of the content string:

<span class="bar">hello</span>


However, it appears that WLW tries to be smart - in a really dumb way ;)
When I switch to HTML view, I can see I ended up with the following markup:

<span class="foo"><span class="bar">world </span></span>


...I really don't see any reason for this. Any idea of a workaround would be greatly appreciated.

Cheers,
Philipp

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