Hey, I have two characters in my campaign that somehow ended up accidentally resetting their ability scores while leveling up, and now they can't get the scores back to what they were.  How is this even possible??  You shouldn't be able to make that big of a change after the character has been created (except by a DM)!  What's more, the level up process should NOT use the character builder for leveling - there should be a separate level up wizard to step you through only what you get for your level and then return you to your character sheet.  

So how do these players get their ability scores back??

I just ran into this too, all my levels are ****ed up now because I selected the wrong feat when I levelled up. I think simply having a "Save" button on levelling up would fix this instead of applying the change immediately. 

Granted this post is a year old, so I doubt they will see this or even care either way. 

I'm not sure I understand your error, given that adding or removing a feat cannot change your levels in anyway. 

So either you're not describing this very well or you made an error.

I've added levels, removed levels, added and removed feats, added and removed whole classes, changed backgrounds, changed races - and none of it affected the base scores. 

Please post a link to your character sheet so someone can look into it for you. (The actual URL, not the “share link.”)