Copy/paste problem

I'm sorry if this has been asked and answered; I tried a search and it didn't work.

I am having a problem with copying and pasting -- when I paste from slide to slide, the weights of lines (including outlines) are changing. Does anyone have any idea why this is happening, and how I can prevent it? The arrows are changing from 5 to 6 px and the outlines of the circles are changing from 4 to 5.

Thanks in advance!