The first three notes clearly have have the length modified.
The last note, still under the slur, does not.
Dorico seems to replace this with a normal note length.
Under Library → Playback Options → Timing → Note Durations, there is a curious note about the last note under a slur:
“Setting the duration for legato notes affects all notes under a slur except the last note, which is shortened.”
Not certain, but my guess would be that the last note of the slur is shortened from 100%, definitely ignoring your 40% setting.
This makes for quite a problem for certain string playback techniques,
as there are many non-legato techniques which are often notated with slurs (for the bow marking, not the legato):
Flying spiccato, upbow staccato, jeté (ricochet), portato etc.