I think there is a genuine problem here.
The Map-Object plugin has been updated in Gimp 2.8 with two new toggles in the GUI ("Create new layer" and "Update preview live") which changes the format and size of the last-vals data stored by the plugin, but the GAP iterator for Map-Object has not been updated since Gimp 2.6.6.
In gimp-gap-master/gap/iter_ALT/mod/plug_in_map_object_iter_ALT.inc
typedef struct
{
GimpVector3 viewpoint;
GimpVector3 firstaxis;
GimpVector3 secondaxis;
GimpVector3 normal;
GimpVector3 position;
GimpVector3 scale;
t_LightSettings lightsource;
t_MaterialSettings material;
t_MaterialSettings refmaterial;
t_MapType maptype;
gint antialiasing;
gint create_new_image;
gint transparent_background;
gint tiled;
gint showgrid;
gint showcaps;
gdouble zoom;
gdouble alpha,beta,gamma;
gdouble maxdepth;
gdouble pixeltreshold;
gdouble radius;
gdouble cylinder_radius;
gdouble cylinder_length;
gint32 boxmap_id[6];
gint32 cylindermap_id[2];
} t_plug_in_map_object_Vals;
-------------------------------------------
But in gimp-2.8.14/plug-ins/map-object/map-object-main.h
typedef struct
{
GimpVector3 viewpoint,firstaxis,secondaxis,normal,position,scale;
LightSettings lightsource;
MaterialSettings material;
MaterialSettings refmaterial;
MapType maptype;
gint antialiasing;
gint create_new_image;
gint create_new_layer; <== THIS IS NEW
gint transparent_background;
gint tiled;
gint livepreview; <== AND THIS IS NEW
gint showgrid;
gint showcaps;
gdouble zoom;
gdouble alpha,beta,gamma;
gdouble maxdepth;
gdouble pixeltreshold;
gdouble radius;
gdouble cylinder_radius;
gdouble cylinder_length;
gint32 boxmap_id[6];
gint32 cylindermap_id[2];
} MapObjectValues;
When you run GAP Frames Modify>Apply filter on layer(s) and select plug-in-map-object, the plug-in runs okay on the first layer but the GAP iterator (which should invoke the plugin for each "tween" frame) then craps out with the following error on the Console:
ERROR: p_plug_in_map_object_iter stored Data missmatch in size 528 != 520
(The mismatch in size is simply the two new toggles introduced, each a 32-bit int.)
The GAP file plug_in_map_object_iter_ALT.inc needs to be brought up to date and GAP re-built for all platforms.
Does anyone know whether Wolfgang Hofer is still maintaining this code (even occasionally)? He hasn't made any updates on git.gnome.org since last July.