When you select a word using a gesture, OSX integrated dictionary opens, but the dictionary find a first word in a text line. For example, In "This is an error." if I select 'error', then the dictionary will open for 'This'.
I observed this problem happened with Writer and Spreadsheet and did not test other applications in Libreoffice, but I expect the same problem may happen in the others.
I think this problem may not be a bug but may be just an unimplemented feature in Libreoffice applications. When a word selected and right click to open the context sensitive menu, "look up (dictionary)" feature is not there.
I think it will improves the usability of Libreoffice if OSX integrated dictionary can be used in Libreoffice applications. So, if this is not bug, it should go to new feature request.
This should be an enhancement request, it's not a bug. (Confirming I see the same behaviour on my Mac.) NeoOffice offers this feature, so perhaps someone could look at how they did it.
Recent versions of Firefox also added that feature and is a wonderful one for those of us learning English. Please, try it. Thank you very much!