Howling:Interfering With Personal Timeline

So it's stated many times by The Doctor (The most glaring and recent example being the episode Fathers' Day in the original reboot) that interfering with one's own personal timeline will have disastrous consequences, cancel out history, et cetera. This is supposedly supported by The Eleventh Doctor in Big Band/The Pandorica Opens, when the two versions of the doctor's sonic screwdriver spark when held near each other due to "temporal friction"; i.e., the paradox of two identical objects being at the same point in space and time, but at different points on the object's timeline. So why is it that, when Rose touched the other version of herself in Fathers' Day, a great catastrophe occurred, but the Doctor is visibly seen to embrace his past/future self, exchange words, and all the rest when he uses the vortex manipulator to sneak away and wire up the Pandorica without the timeline negating like it did prior?110.175.4.178 12:10, September 17, 2011 (UTC)