So the “proper” way to do the next drawing is to start with a blank and use the lighttable – and trace the part you need to reuse. This way you do not multiply the data – and you won’t have any problems. Of course the lasso works as well as long as you don’t keep lassoing, stamping, lassoing, stamping, and so on many times in the same drawing.
I do appreciate that some people like to use the lasso a lot – especially of course if you are using your mouse. This is why we have now made an option for the user to drop the built up vector data. This will completely take care of your problems in your situation. You will not be able to transform and scale without some degradation/blurring (normally you can scale all you want and all lines keeps crisp and clear), but at least you will not have this locked up situation.
This will be part of our next release (alpha 8) coming soon.