configure does not understand OPENGL_ES2_LIBS= variable assignment

Quoting config_help.txt:

Configure understands variable assignments like VAR=value on the command line.
Each uppercased library name (obtainable with -list-libraries) supports the
suffixes _INCDIR, _LIBDIR, _PREFIX (INCDIR=PREFIX/include, LIBDIR=PREFIX/lib),
_LIBS, and - on Windows and Darwin - _LIBS_DEBUG and _LIBS_RELEASE. E.g.,
ICU_PREFIX=/opt/icu42 ICU_LIBS="-licui18n -licuuc -licudata".

--list-libraries output:

...
opengl
opengl_es2
openvg
...

Running `./configure OPENGL_ES2_LIBS=whatever` produces the following output:

ERROR: Invalid command line parameter 'OPENGL_ES2_LIBS=whatever'.

Running `./configure OPENGL_LIBS=whatever` produces the expected output, ie configure does not complain about the invalid command line parameter and procedes with configuration.

Edit: this also affects git development version at time of writing.

Edit 2: the same thing happens if you try to set QMAKE_LIBS_OPENGL_ES2. Completely made up QMAKE variables work fine.