I tried out both of your issues: typing "hahahahaha" a whole lot, and it never missed a beat, and I was going extremely fast.
I also tried out the F/J key thing, hitting one, then hitting the other. Always registered both. Now, sometimes it wouldn't print the first til I let off the second, but it still printed them correcting and in the right order.
Haha would work as its across the keyboard, did you try f/j in portrait? Thats where I saw with those letters. In landscape letters like j/g have issues. Try any two keys within one or two keys of each other by holding one and tapping the other, only the second tapped letter will show (at least on my droid)