Midi Export - problem exporting dynamics

I've had a problem playing back midi files exported from Musescore, in that the dynamic settings are not what I expected. The problem occurs when I amend the default settings for dynamic markings in the score. I've created a simple score to demonstrate the problem. I've used the inspector to change the default dynamic marking values as follows:

p mp mf f ff fff p
48 49 50 51 52 53 54

I've then exported the score from Musescore as a midi file. Using a midi editor (Sekaiju) I see the following (selected) events which shows that the default dynamics have been used, not my amended values:
Note-On G3 49
Note-On A3 64
Note-On B3 80
Note-On G3 96
Note-On G3 112
Note-On A3 49

I get similar problems when trying to use the velocity offset field for the note itself, in that any changes I make to the value are ignored in the midi output.

I've used a recent nightly build, and the problem still occurs there.

Am I missing something / doing something wrong, or is this possibly a fault with Musescore?

Thanks in advance for your help.

Musescore version: 2.1.0
Windows 10 v1709