Bones pretty much hit the nail on the head there. It's a limitation I believe of the ActiveSync implementation of contacts and VCARD versions. Outlook, if you have messed with contacts in that, has the exact same limitation. You can only have a certain small number of (inadequate, IMO) phone or email entries per contact. There's no such thing as a "custom label" in Outlook, and I'm pretty sure that follows suit with Exchange Server and what it is expecting or able to store in its contact format/database. The point: Blame Microsoft, there. Their contacts system is insanely antiquated. As I was complaining at some point -- they have stupid entries like PAGER and RADIO -- but they only will allow for
1 mobile. Asinine. It's almost 2012. I know people with several mobile numbers, counting like... Google Voice going to their mobile, etc. So I ended up having to put those in fields like PAGER or ASSISTANT.
Now... here's the thing. There's iCloud now... which will let you create as many custom labels as you want. Your problem was not the result of iCloud limitations -- it was the result of Google's limitations, which were actually the result of Microsoft's software limitations! Long chain of blame, I know... but that's the truth of it.
I couldn't wait for the day that Google finally supported CardDAV. The last time I checked, their help files said it was being worked on but had no ETA. They do support CalDAV though.
At present, I believe (I could be wrong) but I believe with the recent upgrade to Google in general, you can go into your contacts and edit and create custom labels for your fields. Whether that's a hack on Google's part, or what, if that's true.
Once again, though; bones gave a solid answer, I'm just backing him up with that.
I would recommend creating an iCloud account, getting all of your information moved over, then not have to worry about those limitations and crap again. You can still use Gmail as your primary mail service, and use CalDAV for your calendar -- the only thing that's gonna be a problem is contacts, but that's why I say make the switch over to iCloud for your syncing. Look in the thread called ... I'll find it, where I go into the details.
There's just so much more functionality in using iCloud that you're missing with using Google as an Exchange Server. It syncs so much more and provides an online over-the-air backup for your app settings, etc. Including your photos, documents, bookmarks, reminders, notes... etc.
Essentially, I use iCloud for all my syncing except for my email. I use Gmail as my email server, and I forward all emails going to my @me.com account over to Google, so I have all my mail in one place.
Here is one screenshot I can provide you of the difference:
If you decide you want to convert it over and need help, I'd be glad to give you a hand, send me a Private Message or something in case I forget to check back here to be sure you can get ahold of me. Not sure if bones has the extra time, but he's obviously knowledgable as well, so if he's willing he might could also help.
Just let us know... or maybe you were just wanting to vent. Either way, I understand, I had the same thing happen to me during migration and I ended getting all my stuff just... f---ed up. I nearly had to re-do my contacts since everything was butchered.
If you're interested in reading further on the issue, I recommend these links for you:
Wikipedia - vCard - Talks about the different versions of vCards, as well as vCard extensions, and the new XML based xCards. There's also something called a meCard... which I'm not honestly sure what the difference is with that...
Understanding Direct Push - This was also interesting to me, it goes into the actual steps/technical process of how Direct Push (ActiveSync Push) works (it's not *that technical or complicated, but it may help explain why they say Push can be worse on battery life than Fetch).
Wikipedia - Push technology - You'd probably only find interest in that if you're higher up in technical understanding of different web technologies and concepts. Though, you may be, so I threw it in here just in case.