The issue is that if we start in a empty line, the context is empty. So if we have:
```
###
|
###
```
We can't tell that we are in a comment or not, so we kind of need to check for the previous context. So, in this case it is fine o go past the original selection, since is the only way to know that we are in a block comment. But in the case that you showed before, it wasn't right to move.