Filters with no log levels selected behave weirdly

[Fs00]

I've noticed that filters that have no log levels selected (which is the default for new filters) exhibit a buggy - or at least counterintuitive - behavior.
An exclusion filter without log levels doesn't filter out any log messages, regardless of the value of the other fields. Conversely, an inclusion filter without log levels never matches a message ("All logs were filtered out" is displayed).
This behavior seems to contradict the "Empty fields will not be used during filtering" notice. If I select no log levels, I expect that the log level won't be used in filtering.