XF 1.5 Multi Quote "Insert Quotes" Button press results in error

[kontrabass]

What did I do to break our multi-quote functionality? Any tips on where to start looking?

I'll have several posts selected for multi-quote, but after hitting "insert quotes" I get this error in the chrome console:

 

[S Thomas]

Well, did you change anything recently? Any JS files, templates, upgrades, addons?