Comment # 5 on bug 1099778 from Stefan Dirsch

When looking at the patch I see:

commit c26f7b71c1783648932ba6e71e18a9af35688474
Author: Sergey Udaltsov <svu@linnie-the-pooh.(none)>
Date:   Mon Sep 15 21:46:29 2008 +0100

    added cz(ucw) and options

[...]

+      <option>
+        <configItem>
+          <name>grp:caps_switch</name>
+          <description>CapsLock key switches layout while pressed,
Alt+CapsLock does the original capslock action.</description>
+        </configItem>
+      </option>

Maybe this explains the issue you're seing?