if the "Source extension" of the "Convert" class of an build tool is choosen
to have a dot in it, like for example "twoonapage.dvi" the constructed filename
via "%source" leads to "mydocument.twoonapage.twoonapage.twoonapage.dvi". This
is due to a second call to "setSource" in the determineSource() method of the
Convert class. The second call leads to a second replacement of the suffix of
the filename with the "Source extension" configured.
The overwritten method "determineSource()" in the class Convert is, in my
opinion, not neccessary.
You can find a fix for this in the attachment.