When opening a PDF in Yosemite's Preview.app, I can select text using the Text Selection tool from the Markup Toolbar. However, if I don't click directly on the text, a blank text box will appear. For some reason Preview thinks I want to add an annotation everywhere I click even though I have not selected the Text tool.
This is a problem in that it signals an edit to the document, thus changing the modification date and creating an auto-saved version with no meaningful changes.
In previous versions of OS X, I could have solved this problem by using:
defaults write com.apple.Preview ApplePersistence -bool no. Yet this does not seem to have an effect in Yosemite.