Negative values basicui/rest


I’m trying work with negative values in openHAB2 and can’t pass through.

I defined sitemap entry like this:
Setpoint item=yamahareceiver2_yamahaAV_7cd4a6dc_volume minValue=-80.0 maxValue=16.5 step=0.5 label="Volume [%d dB]"

When I go basicui and tap on down button nothing happens besides background server response like this:
HTTP ERROR 400 Problem accessing /rest/items/yamahareceiver2_yamahaAV_7cd4a6dc_volume. Reason: Bad Request Powered by Jetty://

and entry in log:

21:03:56.197 [WARN ] [] - Received HTTP POST request at 'items/yamahareceiver2_yamahaAV_7cd4a6dc_volume' with an invalid status value '-50.5'.

Could you point me what I’m doing wrong?