Maneuvers to change Ap/Pe seem to be miscalculated

[endrjux]

MechJeb Version

2.15.2.0 (release, CKAN)
2.15.1.0-1543 (dev release, CKAN)

KSP Version

1.12.5.3.3190

Description

After updating to MechJeb 2.15.x I noticed that simple maneuvers seem to be somehow miscalculated now.
Maneuver-planner-created burns to change Ap or Pe result in Ap/Pe vastly different than requested. Planning circularization also results in a wrong orbit. Additionally, because of this, Ascent Guidance (classic) puts rockets in wrong orbits (Ascent itself is ok, the final orbit is different than requested though).

Last MechJeb version in which this worked correctly for me was 2.14.3.0. I tried all 2.15.x release versions, plus some dev versions, including the latest one available in CKAN. In 2.14.3.0 burns were calculated perfectly. (I removed all .cfg files in MechJeb' PluginData dir before the update to make sure old configs don't mess up something)

Replication Case

1. Put something in an orbit.
2. Use the Maneuver Planner to change Ap/Pe.
3. Observe post-burn Ap/Pe.

1. Put something in an eccentric orbit.
2. Use the Maneuver Planner to circularize.
3. Observe post-burn orbit.