I have a Juniper card too and had issues with them holding payments!!! Mine is my best points card, so I stopped charging to other cards, including my debit card and started using that, I didn't much care that the credit limit was $500 - figured i'd pay it off, ensuring the balance was low or $0 at reporting time and keep charging! WRONG...
I called and asked them what the deal was - I'd make a payment and it wouldn't post for 5-10 days... The rep said they do this to ensure the funds would clear and until I made a few more payments through their system it would continue doing this.
Keeping in mind I was making a payment about once every 7-12 days, by the 5th payment or so payments started hitting next business day or same day (not sure what the time cut off is).
On a side note, I haven't figured out how they report - they're certainly better than HSBC, and this may just be that i'm not paying close enough attention, I can never pinpoint when i had a particular balance the day it reports, because of that i've reduced my usage on that card... For instance, my payment would be due on the 25th, my statement would be dated the 5th. I've finally just left it at this: payments made between the 25th and 5th do nothing for your credit reporting!!!
In either case, I've since switched back to using my debit card unless timing is perfect - too bad I wanted the travel points!!!!!