It seems like there may be some race condition in showTextDocument where if it's called multiple times before the previous has completed, each call returns the last editor to be opened.

Here I have an array of two items short_test.dart and short2_test.dart and I call openTextDocument and showTextDocument for each. However the resulting editors both point at short2_test.dart:

The results from openTextDocument are correct in both cases, it's only showTextDocument that seems to be misbehaving.