1. Choose "Reports->Assets & Liability->Investment Portfolio". This generates
the portfolio report normally.
2. Push the "Option" button.
3. Change the value of "Share decimal places" from 2 to 3.
4. Push the "Apply" button. GnuCash now gives the error message:

     Report error
     
     An error occurred while running the report.

The shell from which gnucash was started shows the following messages:

In unknown file:

   ?:  5* [#<procedure #f ()>]
In /usr/share/gnucash/guile-modules/gnucash/main.scm:
 248:  6* [lazy-catch #t #<procedure #f ()> #<procedure dumper (key . args)>]
In unknown file:
   ?:  7* [#<procedure #f ()>]
In /usr/share/gnucash/guile-modules/gnucash/main.scm:
 249:  8* [apply #<procedure #f ()> ()]
In unknown file:
   ?:  9  [#<procedure #f ()>]
In /usr/share/gnucash/scm/report.scm:
    ...
 389: 10  (set! html (gnc:report-render-html report #t))
 389: 11* [gnc:report-render-html # #t]
 357: 12  (if (and # #) (begin #) (let # # doc))
 364: 13  (let ((template #) (doc #f)) (set! doc (if template # #f)) doc)
 367: 14* (set! doc (if template (let* # # # ...) #f))
 367: 15* (if template (let* # # # ...) #f)
 368: 16  (let* (# # # ...) (gnc:html-document-set-style-sheet! doc stylesheet) ...)
 370: 17* [portfolio-renderer #]
In /usr/share/gnucash/guile-modules/gnucash/report/portfolio.scm:
  99: 18  (let (# #) (letrec # # #))
    ...
 173: 19  (let (# # # ...) (gnc:html-document-set-title! document #) ...)
 195: 20* (if (not #) (let* # # # ...) (gnc:html-document-add-object! document #))
 196: 21  (let* (# # #) (gnc:html-table-set-col-headers! table #) ...)
 238: 22* [table-add-stock-rows # # # ...]
 112: 23  (let ((share-print-info #)) (letrec (#) (set! work-to-do #) ...))
 113: 24* [gnc:share-print-info-places 3.0]
/usr/share/gnucash/guile-modules/gnucash/report/portfolio.scm:113:11: In
procedure gh_scm2long in expression (gnc:share-print-info-places (get-option
gnc:pagename-general optname-shares-digits)):
/usr/share/gnucash/guile-modules/gnucash/report/portfolio.scm:113:11: Wrong type
(inexact) argument in position 1: 3.0