Create command should reject incorrect types for known options. It's easy to accidentally provide the wrong types for a "create" option, like providing a string for "max":

MongoDB Enterprise > db.createCollection("test", {capped:true, size:10, max:"10"})
{ "ok" : 1 }
MongoDB Enterprise > db.getCollectionInfos()
[
	{
		"name" : "test",
		"type" : "collection",
		"options" : {
			"capped" : true,
			"size" : 256
		},
...

Or forgetting the "capped" option but including "size" and "max":

MongoDB Enterprise > db.createCollection("test2", {size:10, max:10})
{ "ok" : 1 }
MongoDB Enterprise > db.getCollectionInfos()
[
	{
		"name" : "test2",
		"type" : "collection",
		"options" : {

		},
...

In both of these cases, the server silently ignores some of the options and creates a collection that, almost certainly, is not what the user wanted. I think it would be an improvement for the "create" command to return an InvalidOptions error instead.

This is semi-related to SERVER-25459 (Create command should reject unknown options) and SERVER-16069 (Input validation on the arguments to createCollection).