Not at all a bug. It's common behaviour when you're winning in blowout situations and you're playing a guy way out of position that the coach will sub him out between the 45-47 minute mark for another one of the starters.
As I think has been said before, only way to guarantee 48 is to only dress 5, then hope for no injury/foul out. 45+ is still pretty good, and easily finishable assuming you can pop him in as backup for a later game that week (and given the amount of blowouts you seem to get, should be a piece of cake).