Shift mode with UC-33e

Hi!
I’m trying to setup a shift mode with an assignable button on my UC-33e, but it doesn’t seem to work: I can jump jump between normal modes while pressing the button I chose, but it doesn’t go in shift mode while I hold it down.
By default behaves as a toggle and switches from 0 to 127 at every press, so I assigned it to cc 146 to give it a press/release value, but it still doesn’t seem to hold the 127 for as long as I press it; it just triggers and stops until it triggers again when released.
I also tried with a note 147 value instead of cc, and it’s the same…

Any thoughts? Thanks!