Hi Hans Anton, thanks for your comment! It sounds like what you are encountering is down to the scaling of the batch rather than the number of turns. For example, if we use a scenario that sounds similar to yours, where you had a 2000-litre recipe batch size that used 2 litres of yeast, and you chose to brew a 4000-litre batch over two turns, where the fermentation stage was set not to repeat. The yeast addition, as you have suggested, would double here on a single recipe stage.
However, this would also be the case if you were to brew a 4000-litre batch over one turn; the required yeast would still double as the ingredient addition has been scaled for the batch size. It sounds like a checkbox setting on the addition along the lines of Would you like to override auto-scaling on this addition? may be useful for you here so that certain additions are not scaled. If this is something that you would like to see added to Breww, it would be great if you could raise this as a feature request and give it a vote!
When you say it is repeated on the PO, it sounds like you are generating this through the pre-brew stock check. If so, this will look at what is required on the scaled recipe, but the suggested feature request could resolve it.
You can override the recipe additions on a batch level, so if the yeast is scaled to the batch size and you want to reduce this, you will be able to do this on the addition on the batch! Cheers!