Ticket #2119 (keyboard configuration is wrongly constructed) created

I have set two layouts:
us (default, basic)
cz (default, ucw)

I expect configuration to be like:

setxkbmap -layout us,cz -variant ,ucw -option grp:caps_switch

but ~/.xsession-errors shows:

SET XKB RUN: setxkbmap -layout 'us,cz,' -variant 'ucw,' -model 'default' -option  -option 'grp:caps_switch' -option 'terminate:ctrl_alt_bksp'

You can see, that -variant is wrongly constructed (ucw belongs to cz, not us).