Upss sorry.
I see it. I don't know if it is a bug or not. But if you create two new tiddler ("New Tiddler" and "New Tiddler 1") and you try to modify the title of "New Tiddler 1" to "New Tiddler ", when you save it, TW shows popup Do you wish to overwrite the tiddler "New Tiddler"?
When you save a tiddler in the editor, it removes the spaces at the end of the tittle.
The conflict appears because "$action-setfield" allows add a field with space at the end of its value. When you edit and save the tiddler, TW create new tiddler because TW doesn't match any tiddler with that title.
Sorry for my english.