Halliday & Matthiessen (1999: 208-9):
Some qualities may occur as depictive (as opposed to resultative) Attribute in a figure of doing & happening; in such instances the quality is very close to a circumstance of manner, as is shown by agnate pairs such as the following:
As always with such closely agnate expressions, while they are semantically related they are not synonymous; we could even imagine a figure such as he walked in drunk quite soberly. But they make the point that a quality, when attached to the figure as an Attribute (rather than to a participant as in the drunken man walked in/ the man who walked in was drunk), is construed as being more like a circumstance. The fact that manner circumstances are typically realised by adverbs that are simply derived from (and in some cases identical with) adjectives is a further symptom of the way a quality may resemble a circumstance.