All of the Skirt/ears/tabs I have seen broken or **** happens during shipment, cylinder removal, or rough handling/dropping when the cylinders are in someones hands.  The cylinder cannot be tilted very much when the cylinders are removed without the cases applying pressure on the tabs.

I have seen a few engines tabs "fall off" while the engine is running.  I am confident that the engine was assembled with **** tabs at some prior time.  When the piston clearance becomes excessive the piston exerts tremendous force on the **** tabs leading to eventual tab failure. 

We find a lot of tabs that have cracks in them that have been running engines.  We notice the cracks when we are cleaning the base gasket surface prior to boring.  We bore cylinders using the cylinder base gasket surface as our reference not the head gasket surface like 80 % of the shops that bore cylinders.  Using a clean burr-free base gasket surface guarantees the bore to be 90 degrees to the crankshaft. 

The majority of the boring equipment that motorcycle shops have do not bore the cylinder square to the boring machines base.  Be cautious if the boring machine the shop is using, looks like a drinking fountain with about a 1 1/2 inches shaft coming vertically out of the middle of the machine.  The good boring bars are usually from the Automotive industry.  Van Norman, Tobin Arp, Sunnen, Kwickway are some of the most popular companies that make high quality boring bars. 

The majority of the Automotive boring bars require the cylinder head studs to be removed and mounted to the boring bar on the head gasket surface unless expensive custom spacer rings are used.  The parallel spacer ring goes between the cylinder base gasket surface and the boring bar insuring "squareness" to the boring bar.