Ahh, have found it only happens when the first line has no indent, then even if you select whole lines the new indent on the first line is not selected. But if the first line of the selection has an existing indent (even one space) the new indent is included in the selection.
Its caused by the `>=` in [this line](https://github.com/geany/geany/blob/ca16aff4c5cb73ccb6b1c9db58389a33ad027e4f...) maybe it should just be `>` but it needs to be determined if its deliberate or accidental before its declared a bug. Anybody know the back storey?