Discovered that several ExtJS translation files contain Unicode byte-order mark (byte-sequence EF BB BF) inside them.
But not at the beginning of the file, but at the middle, right after ExtJS header comment:
Found this in the following files:
* Ext JS Library 3.0.0
* Copyright(c) 2006-2009 Ext JS, LLC
* Ukrainian translation
* By zlatko (utf-8 encoding)
* 3 October 2007