The Duplicity of the Thai Visa

When I obtained my Thai Visa from the consulate in Denver I was told that it was a 90 day Visa that I could extend for another 30 days. "No problem" I thought. I planned my vacation accordingly and I had tickets leaving the country a day or two in advance of 120 days.

However, this is not the case when you arrive in the country. The first Visa I got was for 90 days rounded down to the end of the nearest month. Making it effectively 87 days. The extension I just got was similar and I was overdue so it became 29 days (See Cambodian posts below). This shorts me 4 days total and I'm adjusting my flight back home, which is another pain in the ass that I will explain later. Phone lines around here are duplicitous as well.

Has any traveler or expat had the same thing happen to them? Is this to be expected? This is my first time outside of my home country, but to be honest I get the impression that the Thais on one end or the other don't know their own system. Like I said it's my first time traveling away from home so maybe it's just that I'm new to the whole thing.