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Select with lasso. Then turn the tool option to "add " (or subtract) and you will no be able to select, clicking is null, does not create a new selection path.
Workaround: switch to rectangle selection then back to lasso and it works.

Best guess. You have not commited the selection.
Make a selection
Commit the selection - Hit enter key  The selection outline changes to 'crawling ants'
Change the selection mode and adjust the selection.

[attachment=5200]

I understand what's going on: the lasso tool is in edit mode until I finalize it i cannot add, or subtract to it...