21.2.36: balloon-help-mode strings truncated

In 21.2.36, the help strings of `balloon-help-mode' are truncated, i.e. there is a right pointing arrow instead of the last character. Same story for e.g. the string which should be displayed according to `display-time-no-mail-balloon'. More oddly, if you press [End] while the help message is displayed, it disappears and if you move the mouse pointer on to another toolbar icon, the end of the help string is shown - with the left side being truncated. [Home] brings you back to the string's beginning. Sorry, no screenshot. I can't move the mouse pointer, otherwise the balloon help window disappears ... ;-) Markus