Bugs 91349 and 92643 are related to this but include specific extraneous details that may obscure the root of the problem.
The problem is that exporting an animated image as GIF produces a static GIF of just one of the constituent images. The latest version of OpenOffice also does this. However, StarOffice 7 does not have the problem. Since all three programs are very similar, it seems that the bug was introduced in the transition from Star to Open and that Libre has inherited it from Open.
This is clearly a dupe.
*** This bug has been marked as a duplicate of bug 48085 ***