The compact command disallows the use of preservePadding with the paddingBytes or paddingFactor options. The error message for this scenario uses a pipe to convey 'or', which may not be universally recognizable by users.

> var cmd = {compact: 'compact', preservePadding: true, paddingBytes: 0};
> db.getSiblingDB('repro').runCommand(cmd);
{
	"ok" : 0,
	"errmsg" : "cannot mix preservePadding and paddingFactor|paddingBytes"
}

Version: b605f98c68a03fd0e65be72f9a22af4f107dee6b