This isn’t an accident. OpenOffice’s sidebar code was copied and incorporated into LibreOffice. The Apache OpenOffice project uses the Apache License, while the LibreOffice uses a dual LGPLv3 / MPL license. The practical result is LibreOffice can take OpenOffice’s code and incorporate it into LibreOffice — the licenses are compatible. On the other hand, LibreOffice has some features — like font embedding — that don’t appear in OpenOffice. This is because the two different licenses only allow a one-way transfer of code. LibreOffice can incorporate OpenOffice’s code, but OpenOffice can’t incorporate LibreOffice’s code. This is the result of the different licenses the projects chose.

Because of the support we've received from open source communities, we've decided to dual-license the code after 18 months