And then you're angry that the Mexicans, who were trying to overthrow Santa Anna when the Texans captured him, repudiate a treaty that he signed giving away a good chunk of their territory in order to save his own skin?
Is that about the size of it?
Wrong. The Mexicans were divided into more than one anti-Santa Anna faction. There were those who aligned with his xenophobic policies against anglos in Texas but found him to be an inept leader at times of convenience while rallying behind him at other times (remember - he returned to power a few years later and certainly didn't make good on his part of the contract then!). These persons were not in revolt against Santa Anna, but merely cast him off at times when he did something they didn't like (e.g. lose a battle) only to embrace him again when he was on the rise.
On the other side of things were the old federalists and constitutionalists who were highly supportive of the Texan cause and were revolting against Santa Anna and his cohorts for the exact same reason Texas was. Their revolts continued throughout the 1830's, though they were not in power on a national level. After Texas became independent it even sent its navy down to the yucatan to help some of these factions out. Mexican politics were truly a mess in the 1830's and oddly your sympathies seem to be flowing toward the one guy who was most responsible for it all.