TL;DR: When you're a great employee but you can't rely on people to actually give references, even if they previously agreed to it, and a new job requires that references actually reply to HR's email to be considered for employment, it sucks.
Venting: Often either when applying to jobs or after a job interview, you'll be asked to supply job references. I asked my current boss, supervisor, and a coworker if I could use them as references, and they said yes. Boss said if she gets a call from a job I applied to, she'll let me know. I provided their work emails/phone numbers.
HR at company I interviewed at asked for references; I provided the 3 at my current job. HR at new company emailed me later saying my boss had forwarded the reference questionnaire to our HR, and our HR emailed company I interviewed at saying this isn't allowed. HR asked me to provide new references, and I provided 3 from my last company (I left there 2 years ago, but these people said I could use them as references back then).
I told coworker at current job never mind because HR said no (but she wanted me to answer the questions for her and I said in good conscience I can't do that). And 2 of the 3 at previous company didn't contact me even after I contacted them.
I was talking with a friend about this, who said it sounds like my boss is trying to sabotage my leaving the department/company. I hadn't seen it that way, but I'm heartbroken and full of anxiety now.