If a part that can be assigned a number is assigned a number greater than 9 (thus going into double digits) only the first character in the number is read.

This results in PISTON_10, PISTON_11, and PISTON_12 all being read as PISTON_1 and subsequently merged with PISTON_1.

Screenshot example:

https://i.imgur.com/1lBG24H.png