Hmm.
I have "recompute feed periodically" on (every 8 seconds. the default) and when something is new it gives a "Show new updates" link.
For me, recomputing happens so fast there usually isn't even a single frame where the text is printed.
I suppose if recomputing happens more frequently, and if it takes a long time to recompute, then having these rendered on top of each other would be bad. I've just never seen that myself.
Are you on an SSD?