[HtoA] Transmission Extra Roughness Parameter locked range

[opdigits]

Hello, in the Arnold for Houdini documentation the following is said about "Extra roughness":

Extra Roughness

Adds some additional blurriness of refraction computed with an isotropic microfacet BTDF. The range goes from -1 to 1, where 0 means no roughness. It is computed as

transmission_roughness = specular_roughness + transmission_extra_roughness.

However, in Houdini (18.5.408) with Arnold 6.1.0.1 (HtoA 5.5.0.2) the "Extra Roughness" float parameter is locked between 0-1 and I cannot specify a value below 0.

Could this be a bug?

[opdigits]

I should mention plugging in a node with a resulting value below 0 works as intended, its just the standard-surface parameter interface.

[Anonymous]

You can edit shaders.mtd loacted in (HtoA\htoa-5.5.0.2_r1582e12_houdini-18.5.462\arnold\metadatafile) and search for :
[attr transmission_extra_roughness] and change the value from

min FLOAT 0
max FLOAT 1
to
min FLOAT -1
max FLOAT 1