dpkg reports invalid character in version number on package 'compiz'

Status changed to 'Confirmed' because the bug affects multiple users.

it would be nice if at least the problematic characters will see reporting.
other than that - where is the naming convention that this rule set arises from?

tracked it down to this lines in the file dpkg-1.18.4ubuntu1/lib/dpkg/parsehelp.c at the end of function parseversion() at line #186:

  /* XXX: Would be faster to use something like cisversion and cisrevision. */
  ptr = rversion->version;
  if (*ptr && !c_isdigit(*ptr++))
    return dpkg_put_warn(err, _("version number does not start with digit"));
  for (; *ptr; ptr++) {
    if (!c_isdigit(*ptr) && !c_isalpha(*ptr) && strchr(".-+~:", *ptr) == NULL)
      return dpkg_put_warn(err, _("invalid character in version number"));
  }
  for (ptr = rversion->revision; *ptr; ptr++) {
    if (!c_isdigit(*ptr) && !c_isalpha(*ptr) && strchr(".+~", *ptr) == NULL)
      return dpkg_put_warn(err, _("invalid character in revision number"));
  }

quick rationale:
no underscores/colon(revision only)/special-chars/others allowed at present for neither version number nor the revision number.

valid design as of now for version item:
* start with a digit.
* continue with digit, alpha or ".-+~:" chars.
* terminate with a zero char.

valid design as of now for revision item:
* start/continue with digit, alpha or ".+~" chars.
* terminate with a zero char.

a sequence of "x86_64" would not work for any these strings => underscore!
a sequence of "3.4.5@home" would not work for any these strings => at-sign!

a sequence of "3:1.45" would not work for the revision string => colon!
a sequence of "3-4-5" would not work for the revision string => any dash! (the warn message would be raised for the first occurrence)

your sequence of "1:0.9.12.2+6.04.20160823-0ubuntu1" does not work => special char included! rectangular box here in the view. it might be some extended OEM char or a UTF-8 char or an unicode char or whatever. either it sneaked in originally, or it was added later on - even a backspace, CTRL+C or line break might be the root cause. You should be able to trace it down on your own.