[racket] Cannot open file in Racket 5.1.2

A related problem that is easy to replicate (I have not reported it
through the submit bug report yet, because I would like to know if
this is some quirk of my installation):

Open DrScheme.
Type Ctrl-= to open a new tab.
Click on first tab.

This causes the following error on my system:

send: target is not an object: #f for method: begin-edit-sequence

 === context ===
C:\Program Files\Racket\collects\racket\private\class-internal.rkt:4605:0:
obj-error
C:\Program Files\Racket\collects\framework\private\text.rkt:1511:24
C:\Program Files\Racket\collects\mred\private\wx\common\timer.rkt:34:38
C:\Program Files\Racket\collects\mred\private\wx\common\queue.rkt:430:6
C:\Program Files\Racket\collects\mred\private\wx\common\queue.rkt:470:32
C:\Program Files\Racket\collects\mred\private\wx\common\queue.rkt:607:3