BundleTransformer.Less isn't processing .less files if variables are out of order

Question

In the process of updating my nuget packages for BundleTransformer.Less from 1.9.20 to 1.9.143 my application's styles no longer appeared correctly.

I tracked the issue to less not compiling a file because of the order of variable declaration and use. My understanding of less says you can define a variable after using it, but it is no longer the case for me. I am able to reproduce with something as simple as

html {
    color : @test;
}

@test:green;

Which works in online less sandboxes for me.

My app builds and serves up the .less file when requested without error, but the contents of the file is just

variable @test is undefined on line 17 in file '/icons.less':
 [16]: html{
 [17]:     color : @test;
       ------------^
 [18]: }

What part of compilation would suddenly enforce a requirement about variable orders?