When copying multiple slides out of a pptx file into a new, empty presentation, under some circumstances, the first slide will be pasted into the new presentation multiple times, rather than a single copy of each of the multiple slides.

Here are the steps to replicate this bug in libreoffice-4.2.5.2-1.fc20.x86_64 in Fedora Linux.

1. Obtain the following presentation (created in MS PowerPoint 2010):

http://www.slideshare.net/mhirsch45/a-switchable-light-field-camera-architecture-with-angle-sensitive-pixels-and-dictionarybased-sparse-coding

2. Open it in impress.
3. Press the new button to obtain a new, blank impress presentation.
4. Select slides 10 and 11 from the pptx presentation.
5. Press ctrl-c or right click in the slide sorter and use the copy context menu to copy the two slides
6. Change to the new, blank presentation window.
7. Press ctrl-v or right click in the slide sorter and select paste to paste in the two slides.
8. Press either yes or no when asked to adapt the format (it doesn't matter which)
9. Note that slide 10 has been copied twice, and slide 11 has not been copied.

This seems to have something to do with slides that are created by duplication in the original powerpoint presentation. In this case, I'm pretty sure slide 11 was created by selecting slide 10 and clicking duplicate slide in powerpoint. Then it was edited.