On Windows, when I hover over the Rev label I get an Tcl error that
[font measure $font $msg]

failed because of $font being empty. And it true you can get an empty font if the default font ist used.

Here is my patch for this


--- psballoon.tcl       2014-01-11 21:19:28.000000000 +0100
+++ psballoon-x.tcl     2014-01-24 21:36:51.933322189 +0100
@@ -74,6 +74,9 @@
         if {[catch {set font [$w cget -font]}]} {
             set font [ttk::style lookup [winfo class $w] -font]
         }
+        if { $font eq "" } {
+            set font TkDefaultFont
+        }
         set ww [winfo width $w]
         set ih [winfo height $w]
         set ix 0