Unequal spacing when changing staff

[Noeck]

Hi,

the following example shows two measures: In the first one 16 16th notes
are spaced equally on the same staff (this looks good).
In the second measure, the voice changes the staff frequently. Each
group of four notes has still an equal horizontal spacing. But between
each of the beamed groups, the space is smaller.

\version "2.19.16"
\new PianoStaff <<
  \new Staff = "rh" \relative c'' {
    \tempo "equally spaced"
    a16 a a a a a a a a a a a a a a a |
    \tempo "groups by four"
    a a \change Staff = "lh"
    a a \change Staff = "rh"
    a a \change Staff = "lh"
    a a \change Staff = "rh"
    a a \change Staff = "lh"
    a a \change Staff = "rh"
    a a \change Staff = "lh"
    a a \change Staff = "rh"
  }
  \new Staff = "lh" { R1 s1 }
>>

Is this a bug of horizontal spacing or done on purpose?

When showing paper columns, I see that the note heads are spaced
equally. Between the 2nd and 3rd note of the measure, the horizontal
space is smaller which is the optical spacing leading to equally spaced
stems within the group. I think the same should be done between the 4th
and 5th note: Equal stem distances instead of equal note head distances,
shouldn’t it?

Can I do this manually?

Cheers,
Joram