It appears that BSS encodes exported HTML files using UTF-8 BOM encoding. This adds extra (invisible) characters to the beginning of the file. Every time I use this exported output into my PHP project and place some server-side code in it, I get the infamous "headers already export, cannot execute blah blah" message, even when the server-side code is (apparently) starting at the very first character of the file. This happens because those invisible BOM characters are actually there at the beginning, but not visible in the editor (I'm using Eclipse, but most other editor also do not show BOM). I spent several hours banging my head against the wall because of this problem.
It would be advisable that BSS exports using normal UTF-8, without BOM, or at the very least it should provide a setting to choose export encoding.