Bug: "/use <inventory#>" breaks with modifier

To reproduce, equip a useable trinket in the first trinket slot and create this simple macro:

/use 13
/stopmacro [modifier:shift]

A normal activation of the macro successfully activates the trinket. A shift + activation does not. Here we can see a clear problem with the macro system.

For consistency checking, change the above macro to specify the name of the trinket. For example:

/use Talisman of Ephemeral Power
/stopmacro [modifier:shift]

This macro works fine... that is to say that it successfully activates the trinket with or without the shift modifier as it should.

The examples in this post illustrate the nature of the problem I have discovered... the ability to use generic inventory slots seems to break in the presence of a shift modifier anywhere in the macro. This is my frostbolt macro where I originally encountered the problem:

# show Frostbolt
/script UIErrorsFrame:Hide()
/use [modifier:shift] 13
/use [modifier:shift] 14
/stopcasting [modifier:shift]
/cast Frostbolt
/script UIErrorsFrame:Clear()
/script UIErrorsFrame:Show()

This does not activate my trinkets on a shift modifier unless I replace the slot numbers with trinket names. I then did some troubleshooting and discovered the more general problem detailed above. I have already submitted this bug via in-game ticket, but nothing has come of it. I am seeking confirmation of this bug and any solutions I may have overlooked that would allow me to reference generic inventory slots while keeping my modifier functionality.