Yep that's the way it works, the system will allocate a seat. You can for a fee select a seat, if there is more than one of you travelling it will not try and split you up, but you might be on a different row if your seat was the last on that row
Another peace of poor IT from (or used by) the bmi group. Although it actively doesn't split people up, sitting a 3 year old in 22A and its parent in 21F isn't exactly helpful. Sorting it out is annoying for the passenger, can be tricky for staff to sort out if the flight is full, and slows down turnaround times. Something like this would be
so simple to remedy with a few lines of code from an IT boffin.
They need to concentrate on getting the simple things correct first rather than introducing even more complicated fare structuring as discussed above... FamilyFly, FlyPlus... eh? Again they are trying to be everything to everyone and complicating matters. For example only now are Easyjet, who are infinitely bigger than baby, entering the 'business fare' market after building up and earning the loyalty of business passengers for years.
It just seems another stab in the dark whereas what the airline actually needs is a massive overhaul and substantial investment.