Just because you tweak your lineup today, that doesn't mean Yahoo keeps it set that way for the next day. A number of factors can be involved that would prevent it from keeping it, such as adds/drops, setting your roster in advance, etc.
Best to set your lineup each day for the day you want it set. If you want someone to start tomorrow, go to tomorrow's lineup and set it. Not hard to do, and then there's definitely no problems that way.
Yes doctor, I am sick.
Sick of those who are spineless.
Sick of those who feel self-entitled.
Sick of those who are hypocrites.
Yes doctor, an army is forming.
Yes doctor, there will be a war.
Yes doctor, there will be blood.....