[mom] CAPTION_AFTER _LABEL ignores alignment rules

[MB2759]

Hi all,

New user here, finding my way around groff and mom. Captions are working fine 
for me unless I use the CAPTION_AFTER_LABEL option in which case alignment and 
other formatting options are ignored.

Here is a minimum working example:

.AUTHOR    "Me
.TITLE     "My title"
.DOCTYPE    BOOK
.COPYSTYLE  FINAL
.PRINTSTYLE   TYPESET
.PAPER     A4
.L_MARGIN     6P
.R_MARGIN     6P
.PT_SIZE      12
.CAPTIONS IMG QUAD RIGHT
.CAPTION_AFTER_LABEL ALL
.START
.HEADING 1 "Introduction"
Lorem ipsum dolor sit amet, consetetur sadipscing elitr.  Sed
diam nonumy eirmod tempor invidunt ut labore et dolore magna.
Aliquyam erat, sed diam voluptua.

.PDF_IMAGE myimage.pdf 5c 5c \
CAPTION "This is the long figure caption." \
SHORT_CAPTION "Short caption."

.END

Expected behaviour:
Figure caption text appears under the 5x5cm image and aligned with the right 
edge of the image.

Actual behaviour:
Figure caption text appears under the 5x5cm image but is aligned with the left 
document margin.

If I remove the CAPTION_AFTER_LABEL ALL option, caption behaviour is as 
expected (above the image and aligned to its right edge).

I've been trying to solve this for days and am going around in circles. Have I 
missed something obvious, or is it a bug?

Thanks