Pressing the insert button correctly drops markers at the playback cursor point while playing audio until ctl+z is used to undo a drop marker operation. The next dropped marker will then be placed at the position that playback started from instead of at the active playback cursor location. The only way to drop a marker on the fly after ctl+z undo is to restart playback.
Thanks for the accurate report. I can reproduce.
FYI, this will be fixed in next update.
I ran into similar behavior yesterday when splitting clips with the “s” shortcut on the fly yesterday. After ctl+z undo the next split does not fall at the start of playback, but one does have to restart playback to drop more splits at the cursor location on the fly. (This is not as frustrating, and is pretty much the way I remember Wavelab behaving back on versions 5 and 6).