The weeks boxes within tasks under goals act strange

I set up tasks underneath goals - but then when I attempt to block out weeks for those tasks - it acts very strange. For example, if I click on week 1 for the first task and then week 3 for the next task - it automatically highlights weeks 2 and 3.  Its then rather difficult (if not impossible) to uncheck week 2.  I am finding this process pretty cumbersome and really not of much use at this point trying to undo what the system is doing - any suggestions?