Btw, 1.37 is not released
Yes its the development version, AFAIK there are no specific fixes.
even 1.36 is not pullable from Ubuntu repos yet
Thats a general problem with distros, they may be slow to release new versions of software, especially LTS distros like 18.04.
I tried a nightly, and Geany seems to use a different theme internally
And does the problem still occur? Geany does not have its own themes, it just uses what the desktop provides (unless the distro patches its releases). Which is why I asked about which you are using (hint hint :) because it won't be the Cinnamon that LM uses.