triggeringItem.state bug?

No. This is how openHAB works.

You must draw a distinction between Item commands and Item states. Clearly they are not the same thing, because you can send command UP to a blind and get resulting state 99%

So commands go on openHABs event bus. They might trigger rules, and get seen by bindings that pass the command along to a real device. At some later time, the device might respond with a new status, and the binding will update the Item state (also via the event bus, so can be used to trigger rules etc.)

A rule triggered by received command should NOT expect to “see” the Item’s state from the result of the command. It hasn’t happened yet. It might happen in 10mS or 10 seconds. It might happen halfway through executing the rule.

In summary, it’s asynchronous.
You need to take care to avoid writing rules that fall into this trap - Items are not regular program variables.
If you are interested in the state, trigger your rule from state events changed or received update.

Oh yes