I've been working very hard in fixing almost 10 obscure bugs in the -O2 and -O3 options. And they finally seems to be fixed. Apenao's game compiles with -O3 flawlessly and plays well (obviously, -O3 includes -O2 optimizations); but I need more testing. So anyone who has programs to test both -O2 and -O3, and check if it compiles and behaves as it does with no optimization at all.
If everything works ok, I expect the compiler will behave more intelligently than ever before. It's been ultra-hard but I hope it's worth the hassle.
You can download .zip or .tag.gz 1.2.5 files, or the MSI windows install: http://www.boriel.com/files/zxb/zxbasic-1.2.5r1513.msi