Oh my gosh. I hate it when you catch that level 6 Pokemon, and then your next random battle is the same one, only at a higher level. Nothing is more frustrating.
You didn't mention it, but I swear that the first Pokemon I always encounter in a new area is a rare Pokemon. Not knowing this beforehand, I slaughter it if its level is not to my liking. When it never shows up again, I cry my self to sleep.