Hi Jürgen, thanks for getting back to me. I'm attaching two files: the MWE polyglossiabreaker2.lyx, and the necessary bibtex file. Put both in the same directory, and it should work.
Or rather, the file will compile with 2.2.2, but not with 2.2.3 (giving back the error about deleting a closing bracket as previously described). Thanks for your help, Andrew
polyglossiabreaker2.lyx
Description: application/lyx
@Book{butcher1917poetics, Title = {The {P}oetics of {A}ristotle}, Author = {Butcher, Samuel H.}, Publisher = {Macmillan}, Year = {1917}, Address = {London} }