The players reach is slightly further in creative mode than survival mode (Untested with mobs)

To recreate (Flat worlds are recommended for this test)
1. Select Creative mode
2. Place a block in front of you.
3. slowly walk backward and stop as soon as you are unable to reach the block in front of you.
4. inch back to the exact point where you can reach the block again
5. enter survival mode
6. The block's outline will disappear when you go into survival mode meaning that the reach in creative is further than the reach in survival

This is a difference of less than a block so it doesn't currently affect gameplay too much but it is still a bug