Bootstrap weird error while recompiling assets

I have this weird mistake where ...

in my application.js file i have

//= require jquery
//= require jquery-ui
//= require jquery_ujs
//= require twitter/bootstrap

if i do

 RAILS_ENV=development rake assets:precompile

my bootstrap drop down stops working. however, if I delete the twitter / bootstrap request and delete the save in my editor, then refresh the page on my local machine. he works again.

I do not understand why. this jquery / bootstrap download has been a problem for several weeks. recompile my assets. it works if I recompiled it, but then uninstall it and refresh the browser

UPDATE

my css uses custom.css.scss. there is nothing special there except

@import "bootstrap";

at the top of the file.

ive went back to scss, not the smaller one, and application.js looks like ...

//= require jquery
//= require bootstrap
//= require jquery-ui
//= require jquery_ujs
//= require_tree .

, ,