I have to steam my spuds as if I boil them they just disintegrate.
It's because of the starch. .I leave them in the ground until the tops go down completely so they end up with a high starch content.It also means they taste fantastic! The starch is also associated with increased water content
Commercial growers usually harvest them early ready for the markets so they don't disintegrate.
Having said that this year was a total disaster. We had buckets of rain in August and I lost 90% of my crop to various fungal rots.