Rotation on almost identical Vectors quite different

Hi there,

Been pulling my hair out on working with vectors and rotations for a few days now and have just discovered something that doesnt make any sense to me, but maybe im missing something obvious

I have 2 vectors that seem almost identical to me

{X=0.000000000 Y=0.000000000 Z=1.00000000 }
    X: 0.000000000
    Y: 0.000000000
    Z: 1.00000000
{X=0.000000000 Y=1.22464679e-18 Z=0.999999940 }
    X: 0.000000000
    Y: 1.22464679e-18
    Z: 0.999999940

However when I call rotation on these two vectors I get significantly different results

{Pitch=90.0000000 Yaw=0.000000000 Roll=0.000000000 }
    Pitch: 90.0000000
    Yaw: 0.000000000
    Roll: 0.000000000
{Pitch=90.0000000 Yaw=90.0000000 Roll=0.000000000 }
    Pitch: 90.0000000
    Yaw: 90.0000000
    Roll: 0.000000000

Is this legit? What am I missing?

Why are the rotations on these 2 vectors not almost identical?

Thanks in advance for any help