Display action button on dashboard

[Djmiles]

I have three tables showing in my dashboard - Devices, Loans, Repairs. To add a loan or a repair to a device, we can select a device in the Devices section, then click on Add in the relevant table. Perfect. 
Except that if the user clicks on the Add button in the Loans or Repairs table without selecting a device first, the form opens up with the Device details empty. 
I'm trying to prevent that from happening.
Here's my dashboard

I can get it to show inline, which is okay if there's no other solution, however that also is misbehaving. According to the guidance, it should show next to the chosen column.

However, this is what I see - it is replacing the column, not showing next to it. (It tries to do this against the Serial Number column but I want to see that value, so here I have it against a different field)

In case it is the action itself that is causing this issue, the Target is

LINKTOFORM("Loans_Form",
  "Device",[SerialNumber])

What on earth am I doing wrong, or have I found some bugs?