Some creatures are partially transparent - is it a bug?

In game (VCMI v 0.93) some creatures are partially transparent (in battle and in town).
For example I’ve attached gnoll, that shoulder is like a hole.
Is it a feature or a bug?
In DEF Viewer these units are shown right without any holes or half transparency.

Can transparency be turned out by some val in configs?
Gnoll (89.1 KB)

Bug, not easy one to fix. Short version - first 8 colors in .def’s have special handling and should not be used outside of their area of usage (e.g. shadow, unit selection and such).

And there is no way to change this behavior.