InDesign CC 2014, 10.0.0.70 Build; Mac Pro 10.9.4 32GB RAM
Recently, I have encountered an infuriating bug working with master pages. When overriding an item and deleting it, another identical item replaces what's deleted. For example, I override a text box in the running foot of my document, hit delete, and another identical text box is in its place. It doesn't matter how many times I delete the content; it's as if there is an infinite number of the same item stacked on top of each other. It doesn't even happen on every page with the master page applied. My workaround, for now, is to apply a [None] master to the page, then paste the contents of the desired master in place on the page.
My co-worker says this also happens to her, but I'd never experienced it until updating to InDesign 2014.