It's a well-known problem and yes, it will likely lead to many UA customers overpaying, which is what UA wants. Has been ongoing for years and since it generated additional revenue there is no reason for UA to fix this problem until they find themselves in a major social media sh!tstorn.
The workaround is to call to re-book. Then you get the lower fares.
Maybe the mods can move this thread to the other reports of these issues.