I also believe this is a glitch, I just booked my routine “next weekend E-fare” from FAT-BOS for $315 all in. As long as you meet the following booking restrictions
1) T Class Available on all flights
2) Depart AFTER 7:00PM on Friday
3) Return on Monday or Tuesday
You should be able to book without any problems for either this weekend on next weekend. Typical example of united.com being unreliable
