Steps to reproduce:
Result => the tag is added into the text field as expected, but with a strange animation sliding from right to left, as if the piece of tag you had typed was being deleted and the new selected tag added, or something like that.
Actually the online demo does not exhibit this issue, but the code downloaded from github does. (this may mean that the bug is a regression introduced in a late update, and that the online demo is not up-to-date?)
This has been fixed in 11d5d68 - appreciate the detailed repro steps, thanks!