Why does "Ctrl + Y' repeating an action not always work?

[pintree3]

I have noticed that repeating a previous action (Ctrl + Y) like making changing the spacing before or after a word doesn't seem to often work within a table. Why is this so, and could this be made to change? I have also noticed that often enough this doesn't work as well even if there are no tables (visible or otherwise). I cut and paste Job Ads from my browser (Usually Firefox) into Word 2010. And yet, I could not repeat an action like the ones described above. The strange thing is that most are from the same website, thus suggesting equal formatting throughout their advertised jobs, and every so often Ctrl + Y does work? What exactly is happening here? I find it bothersome to have to go to place after place and R-click, choose 'paragraph' wait for the window to open, Click here and there to change the settings, cliik ok--a 4 to 6 step process again and again while a simple ctrl+Y can make you do so in just 2 steps (By selecting all the instances at once(Ctrl + left click)--2 steps instead of 50. Any explanations as to why this happens and how to go around this would be greatly appreciated.