Steps to Reproduce

run the attached example choose-when-without-otherwise-ZK-3830.zul
choose "green" from the combobox
choose "red" from the combobox
choose "other" from the combobox

Current Result

green -> green button is rendered OK
red -> red button is rendered OK
other -> the previously rendered button remains

Expected Result

consistent behavior:
green -> green button
red -> red button
other -> no button at all

OR

in case <otherwise> is a mandatory element (for a technical reason) throw an exception to indicate incorrect usage

Debug Info

when setting the initial status value to anything other than red/green no button is rendered as expected.
Only when switching from a matching <when> block back to a non matching value the previous <when> block remains

Workaround

1) add an empty <otherwise/> element
2) surround the whole <choose> element with an <apply> to re-render the whole <choose> element and contents (like initial rendering)