I found a bug when placing partially overlapping blueprints containing reinforced or classic nixie tubes (it doesn't occur with small ones). If you configure a nixie tube with a signal and copy it, you can't paste it on top of itself or on top of other identically-configured nixie tubes (trying shows the message "reinforced nixie tube is in the way). A workaround is to use force-building, but it seems like that shouldn't be necessary.

Thanks for the report. I've reproduced and fixed the issue. As soon as GitHub Actions works again I'll update the mod.

Done! Please let me know if find any other issues.