System:hysteresis profile UNDEF state of switch

When system:hysteresis profile is used in item binding Switch item is being set to UNDEF value if received value from channel is between “lower” and “upper” values.

Documentation states:

// Triggers a temperature high alarm (Switch = ON) as of 30 °c and stays ON until temperature drops below 29 °C
Switch Outdoor_Temperature_High_Alert { channel="openweathermap:weather-and-forecast:api:local:current#temperature" [profile="system:hysteresis", lower="29 °C", upper="30 °C"] }

As I understand that should mean if value is above “upper” switch is set to ON, if below “lower” - set to OFF and if in range “lower”-“upper” switch state is NOT changed. But in fact it’s being set to UNDEF.

Is it bug or documentation is wrong?