un-trash button

Yes there is issue with trash button still appearing. It's because this module doesn't know if node is trashed, it simply doens't store it's state. It seems like minor issue because "trash" operation in most cases available to privileged users such as admins or moderators and they can be aware that button doesn't hide. You can simply insert some action which will mark this node ( for example, using Flag module, or Workflow module) so your privileged users will still see button but will be aware of the state.
I was going to implement that, but decided to leave "marking" of trashed node to site admin. Implementing states would duplicate functionality of Flag module, and I intended to keep Trashbin as simple as possible, so I decided to not implement this in Trashbin and instead wait when Flag implements access control so Trashbin would become simply "button" flag type for Flag.
I am watching Flag development, so in case Flag access control will never be implemented in reasonable timeframe, I will advance Trashbin so it will store and use node states.

You can hide it yourself, just implement hook_form_alter() which checks workflow state (for example) and removes "trash" button from the form depending on node state. I will not do it myselft because I think state must be stored inside "marking" module, in our case Trashbin itself, otherwise it has to support fetching node state outside of _every_ integration module.
And if I get state only from Workflow module it will make Trashbin less flexible and make it depend on Workflow, which wasn't my original intention.
In case you can't program it yourself, you have only option to wait :) or find other solutions..

something like this:

function yourmodule_form_alter() {
  if ( node form check and workflow state check here ..) {
    unset(button form element here..);
  }
}