Debian revisions should be stripped from versions in symbols files. Not doing so leads to dependencies unsatisfiable by backports (1.0-1~bpo << 1.0-1 while 1.0-1~bpo >= 1.0). If the Debian revision can't be stripped because the symbol really appeared between two specific Debian revisions, you should postfix the version with a single "~" (example: 1.0-3~ if the symbol appeared in 1.0-3).
This problem normally means that the symbols were added automatically by dpkg-gensymbols. dpkg-gensymbols uses the full version number for the dependency associated to any new symbol that it detects. The maintainer must update the debian/<package>.symbols file by adding the new symbols with the corresponding upstream version.