You’re not crazy. This does work cleanly on revenue tickets, but award tickets are a different story and JetBlue has never really fixed it.
What you’re seeing is normal behavior unfortunately. The “change flight” flow often shows a 0 point difference even when the award price clearly dropped. The system basically treats it as an even exchange unless there’s a cabin change or fare type change. It’s been like this on and off for a while.
The only reliable way to get the points back is exactly what you said:
cancel the award
rebook at the lower price
As long as it’s a Blue/Blue Extra award and not some weird partner thing, the points redeposit instantly and there’s no fee, so it’s safe, just annoying.
Calling in usually won’t help much. Most agents will tell you to cancel and rebook anyway. Some can manually reprice it, but it’s hit or miss and often takes longer than just doing it yourself online.
So yeah, not a glitch you’re doing wrong. Just JetBlue award IT being JetBlue award IT.