renegotiate rent 12 months into a 24 month agreement

My landlord recently asked me for a nearly-20% increase of my rent. I know this is normal in HK, I've lived here a long time and signed many leases in my time. However, it's the first time that I've ever had a landlord ask for more money at the half-way point of my first 2-year agreement. I believe what he's done is legal, since I asked for a 12-month break clause. The landlord initially wanted a 'fixed' 2 year lease, now that he's done this I am kicking myself for being scared of a fixed 2-year commitment. I gave him a counter-offer of half the ridiculous 20% he was asking for, which he agreed to. A couple of questions remain, which I would love some answers to if you have any experience or opinions on the following:
How common is it for a landlord/lady to renegotiate rent after only 12 months in, on a 24 month agreement with a break clause?
Is the rental market still going up, to the extent that a landlord would try for a 20% increase at the first possible opportunity?
Should I take this as an indication that he will ask for more money at the 24-month stage, and every other opportunity he can find, and try to find a more reasonable landlord?
What exact wording should I be looking for in my next agreement, to ensure that I can break the lease with a 1 (or 2) month notice period, but which doesn't allow re-negotiation of the rental amount?
Thanks. I've been getting a variety of answers so far from people, so am quite confused by this all.

I'm only a small investor, but I can offer the following:

1. the rental market varies a bit depending on which part of HK you are looking at as well as the size/quality of the unit. My experience is in Mid-Levels and over the last year or so my experience has been that rents for smaller properties in Mid-Levels have been flat to slightly higher. If you are in this part of the market a 20% increase suggests either that you were paying well below market rent when your first signed the lease or the landlord is trying it on. I assume you did your research before agreeing to the increase?

2. my preference as a property owner is to keep my properties occupied and the cost of dealing with even a short vacancy + agency fees + touch up repairs between tenancies is usually a lot more expensive than missing out on a small rent increase. I usually start by asking for 2 years fixed term but will accept break clauses after the first year if it is two-way. The language is usually very simple: "Either party may elect to terminate this lease before the expiry of the Term by serving not less than [two] months' written notice on the other provided that no such notice may be issued before the date falling [twelve] months after the commencement of this Lease." (or similar)

3. I have never put a clause in one of my leases that allows for the rent to be reviewed during the term.

4. If the relationship is not working, look for another place, give notice and move out. Unless you have some unusual requirements, were are plenty of choices out there.

Thanks Trainee Investor!
I am in the under-20k market, and do my research very carefully since a decent apartment in that price range is very hard to find in the neighbourhoods I like (I refuse to live in anything smaller than about 450sq ft, which makes it harder).
The apartment was a bit of a good deal initially, but I had several things going in my favour... I'm a desirable tenant in other words as a single, non-smoking teacher-type. I have added to the value of the property by installing attractive lighting, new curtains, a bigger fridge, and better tap fixtures.
Due to it being a bargain initially, I can accept the 1.5k agreed increase, but I agree with your 4th point, and will be looking to move at the end of the 2 years because it's pretty clear I'll be having to fork out for another increase at that point in time.