I noticed a very annoying glitch . When i have a quest with 2 or more sims and switch to another sim all the sims in that area will go home or leave someplace.. it also hapends on free mode also my sims are constantly bumping into things and each other because their is hardly any room for them to walk

it doesn't sound like a glitch it sounds like your free will level is set high, sims will go home if they are sleepy or have no one to interact with in the area, happens when there task queue is empty, if it is happening with a full task queue thats another issue.

The other thing about bumping into people and things its a routing issue, it will happen in ts3 if they can't go where you intend them to go, they get upset and drop the task of going that direction, try moving objects in the room around to create more floor space, i find this happens allow when sims group up like at the reception halls and tavern.

Hmm. Quest important sims generally get tied to a given lot, like one of the Hero buildings, the Judgment Zone, or town square. This can misfire sometimes when a quest objective requires the Sim to move to a different lot. The King's Ball part of the annex Quest for Advorton seems very prone to this, at least in my case.
NPC sims also don't seem to care about what time I set to give sermons at, they seem to gather at all four times... but only when one of my active heroes is a priest.

I remember someone mentioning about how in TS3, those sims not in an active family would exhibit stalker-like behavior to keep the neighborhoods populated withg Sims the player could encounter. I wonder if this carries over to TSM. There does seem to be a curfew in effect where most of the NPCs will return to the Village rabbit-hole at night.

Anyone else have observations on mass NPC sim behavior? (Other than eating your food, stealing your drinks, and being annoying.)

There was a one -really- frustrating bug in the Invasion quest where the invading NPCs were all bandits. My Knight couldn't get near the leader I was supposed to defeat for all of them threatening her for money... and even each other. I couldn't even get into a duel to lay them all out because the theaten interaction interrupts the victim.

In regards to routing issues, I try to leave at least two squares on the building grid between any two objects I want sims to be able to move around. A carry-over habit from TS3.

I have encountered an odd bug where certain points of the map got blocked off somehow, at the top of sloped pathways such as from the Docks to the Castle and the path up to the Churches.
There was a small line where the "Walk-to" mouse icon would change back to the the "No interactions available" icon. Sims just couldn't route around it, and pretty much any action I tried to get them to do which required them to go past it would fail.
It has only occured in the one Kingdom so far though, thus I'm chalking it up to a corrupted save distorting the landscape.