I created a new tab control in LV7.1 and that little button does not work for me either. The control seems very querky when I play around with the settings.
Yep - It's a bug and will be fixed in the next release (along with some other unfortunate behavior related to these settings). Thanks for letting us know.
In the meantime, possible workarounds are:
o Keep the tabs on top o Change to Allow multiple rows o Implement your own inc/dec buttons