So, I need to fix a lot of old files, that worked just fine, tab order was set in InDesign and PDFs were created using FormMaker 3.1.0.
Now I`m using FormMaker 4.0.12. Tested it with no changes (opened old file and created PDF). When I open PDF and check Radio buttons tab order, it is correct. When I apply Edit -> FormMaker, the order changes.
In normal cases, when it is just a few buttons, the order is reversed (1 2 3 is reversed to 3 2 1).
In complex cases, when it is 2 sets of 3 buttons each with the same name and works in unison, the order is mixed up.
Everything works fine with the new file, just tested it.
According to my observations, when I click Create Interactive PDF in FormMaker, the radio buttons change their appearance. Maybe script recreating or modifying them.