Motion frame pasting are extreamly laggy

when paste a new frame on motion frame, the time it take grows as the number of total frame.

for example, it takes 2 second to paste a frame if there is 30 frames in total. and it take 5 second if there is 60 frames. this shouldn't happened because every pasted frame should be equal. so if there is 10 frame to paste in the 60-70 frame, it will take at least 1 minute waiting. no counting the useless "smooth" animation in the program make every movement even slower.