version:1.1.30, build 58304, win64
vanilla, no mods, used editor mode to reproduce but not necessary
steps to reproduce:
- put rail and station as shown in image:

- put red train and wagon for it connected by hand, auto positioned at station
- put blue train and wagon a little away by hand, or bots
- put the signal just at the edge of red train, shown above. I highlighted it
- set the first station of blue and red train to the station available.
- put some fuel to blue train and set it auto. blue train shall travel to the edge of signal and stop there, as expected.
bug:
- select entire screen content into a blueprint.
- be sure to check trains in blueprint
- put it elsewhere, using bots
result: when bots put the trains the entire 2 loco and 2 wagon shall be connected making it single train
expected: these are two different trains when blueprint was created and they should be separated.
I cannot see or understand if blueprint is created with connection or bots put the trains connected.
note: train length does not matter, I realized it in single direction L-2W-L trains but it can be reproduced with L-W as you see
this is the first version I encountered this but it could be an old issue.