While not technically speaking a bug, this can be confusing, see example 1 below.

Line numbers should rather represent the position where the problem starts, not the position where the problem ends. Given that the message returned with the position includes the portion that triggers the error, it should be relatively easy to return the starting position.

Example 1: checking
@unknown {
 p {
  font-size: 2em;
 }
}
... returns "5 Parse Error @unknown { p { font-size: 2em; } }", pointing out that the problem occurs at line 5. I'd expect 1.


Example 2: checking
p {
 unknown:
  10em;
}
... returns "3 p Property unknown doesn't exist", pointing out that the problem occurs on line 3. I'd expect 2.