ANNOYING RMXP GLITCHES-- IS THERE A CURE?

For reasons that I cannot fathom, sometimes odd glitches plague my games. For example, sometimes the game arbitrarily decides that certain tiles, such as walls, are now permeable, and players, or moving events, can walk right through them. When this happens, it's not all the tiles of a particular sort, either-- it's just two or three squares here or there, on one map only. (One time, it did the opposite-- it decided that all the grassland tiles on a given board were walls, or something, and nothing could move.)

The only solution I've found is to redraw the tiles on a higher layer-- erasing them and redrawing them doesn't eliminate the problem, annoyingly. It's as if the game decides "This section of the map is, or isn't permeable, and what you put there doesn't matter."

I've also run into a glitch where telling it to change an event to a specific graphic doesn't work-- it changes the event to a different graphic than the one I specify. Incredibly annoying.

I'm using a legal copy of RMXP, on Windows XP, with quite a bit more RAM than the system requires.

Any ideas why this happens?