I have never heard of this 'molasses' theory ... and seriously doubt it.
Maduro (and oscuro) leaves are moisted and allowed to ferment in large containers until they turn a dark, rich, brown (or almost black) color.
Then the leaves are bundled together, and are put into large piles, called burros. To reach the high temperatures necessary for proper fermentation, these piles, called burros are six feet high.
They are exposed to a much higher temperature, usually 108 degrees (42 C), for a much longer period of time, which can be up to 60 days. The leaves on the outside are rotated with those on the inside to ensure even fermentation.
This process is monitored even more closely than the first fermentation process, because if the middle of the burro goes above 108 degrees, the leaves become abnormally dark, and their flavor profile becomes radically different.
Sometimes the leaves are exposed to higher temperatures for even longer periods of time. These leaves are typically wrapper leaves, and these wrapper leaves almost always are maduro (dark brown) or oscuro (black).
Many oscuro wrappers produced for the US market use a process called “cooking,” where the fermenting leaves are placed as bundles in an oven that is heated to 120 degrees, creating a wrapper that is dark as night itself.