Yes, you need to be very specific in the order that you define the parameters of your items. It HAS to be:
ItemType item_id "itemName" <icon> (group) ["tag"] {binding}
Real example:
Switch bedroom_fan "Bedroom Fan" <light> (gBedroom) ["Switchable"] {insteonplm="xx.xx.xx:F00.00.02#switch"}
If you put the item parameters in ANY other order, openhab will silently fail, and moreover, any items defined after that item in that same items file will be ignored. At the very least, the error is not reported with the default log settings.
This is touched on in the wiki, but that needs an update. It does not cover square bracket [“tags”] for HK/HE - in fact it uses square brackets to denote “optional” items which is just confusing. Also it does not mention the fact that this syntax is strictly enforced.