In the future I suggest using the Bug Tracker, but yes I am familiar with this issue.
I haven't had the chance to figure out why it happens, but Beta 1.7.3 seems to be a bit weird when it comes to chunk loading on login in combination with AuthMe. Unfortunately AuthMe is a requirement for any sort of security since there's no premium checks in that version anymore.
Generally the only way to get around it (that I know of) is to install Zombe fly mod, and immediately after joining enable fly, then run /login <password> and from that point you can turn fly off and play normally.
It's an annoying issue, I know - but it's basically that or have zero server security
If you can't be bothered to install Zombe (or if you aren't familiar with how to do so), you can grab this download which has a pre-modified version of Beta 1.7.3 with Zombe and a couple other fixes added.