"...if I minimize the window (Drag it to the side of the screen)..."
I'm not 100% sure, but I think you probably mean "re-size" rather than "minimize".
"...under Timeline in the first event box the year appears partly below and partly on top of the box title (Birth). All other boxes appear as they should and the problem is not there with the window maximised."
Page rendering problems are quite often browser specific and might be user-option generated.
First, what browser are you using when you see this rendering problem? Do you see the same problem repeated if you utilize a different browser?