This game has invisible achievements in development mode and it can be patched to make them work. Please refer to the
broken achievements thread, section
BROKEN ACHIEVEMENT FIXES in the OP for further information about this.
The direct link to grab the patch is
here. It includes a readme that tells you how to install it.
As Studio Élan's other games have recently received updates and (yet unsupported) achievements, I'm positive this will be taken care of by an official update in the near future. Highway Blossoms does face a technical hurdle unique to the bunch though.