Molecular geometry optimization of methane and ethane was done using the program Abalone.

Methane (before optimization):

C-H bond length: 1.77376218

Bond angle: 109.47119855

Methane (after optimization):

C-H bond length: 1.09

Bond angle: 109.47122067

Why did the value of the C-H bond of methane go from a messy number with many digits, to such an exact number with only three digits that are not zeros? Why didnt the angle change as well?

Ethane (after optimization):

Average C-H bond length: 1.09030685

C-C bond length: 1.53169302

H-C-H bond angle: 109.41768251

H-C-C bond angle: 109.52470540

Why did the value of the C-H bond of ethane NOT go from number with many digits, to such an exact number with only three digits that are not zeros?