Tuxguitar behaves as if Control key is pressed for keyboard shortcuts

When working in Tuxguitar, pressing any key which has a Control-<key> shortcut assigned to it in the shortcuts list, the Control-<key> action occurs instead of the <key> action. For example, when pressing the "2" key to insert a note, the second voice (assigned to Control-2) is selected instead; When pressing "o" to make the current note a ghost note, the save-before-opening-a-file dialog (assigned to Control-o) appears instead.

Ubuntu 13.04

apt-cache policy:

tuxguitar:
  Installed: 1.2-15
  Candidate: 1.2-15
  Version table:
 *** 1.2-15 0
        100 /var/lib/dpkg/status
     1.2-14 0
        500 http://il.archive.ubuntu.com/ubuntu/ raring/universe i386 Packages

default-jre:
  Installed: 1:1.7-43ubuntu4
  Candidate: 1:1.7-43ubuntu4
  Version table:
 *** 1:1.7-43ubuntu4 0
        500 http://il.archive.ubuntu.com/ubuntu/ raring/main i386 Packages
        100 /var/lib/dpkg/status

openjdk-7-jre:
  Installed: 7u25-2.3.10-1ubuntu0.13.04.2
  Candidate: 7u25-2.3.10-1ubuntu0.13.04.2
  Version table:
 *** 7u25-2.3.10-1ubuntu0.13.04.2 0
        500 http://il.archive.ubuntu.com/ubuntu/ raring-updates/main i386 Packages
        500 http://security.ubuntu.com/ubuntu/ raring-security/main i386 Packages
        100 /var/lib/dpkg/status
     7u21-2.3.9-1ubuntu1 0
        500 http://il.archive.ubuntu.com/ubuntu/ raring/main i386 Packages