stock_forecast does not spread all the quantities
Stock forecasts allow the user to specify the quantity to be spread as well as the minimum quantity per day but the current algorithm will usually result in spreading "quantity - minimum" instead of quantity.
To be more precise:
There's an algorithm that creates an array of the days and assigns the number of minimal quantities to be spread (1 for each minimal quantity): https://hg.tryton.org/modules/stock_forecast/file/tip/forecast.py#l522
Later a stock move is created for each day where the number of minimal quantities is greater than zero: https://hg.tryton.org/modules/stock_forecast/file/tip/forecast.py#l499 and the number of minimal quantities is multiplied by the minimal quantity.
This means that if we have a forecast line for product X with quantity = 100, minimal quantity = 50 and executed quantity = 20 the algorithm will only spread 50 in the day of the middle of the period: https://hg.tryton.org/modules/stock_forecast/file/tip/forecast.py#l534
Instead, I propose that we ensure that all the pending quantity is always spread, assigning it to the first day of the period.