From OpenSCADAWiki
Buttons are currently generated dynamically by copying the first and only, according to the virtual pages of the signal objects in the project tree, with the serial digital identification from 1 (one). The limitation on the number of buttons or signal objects is only the total length of the names of the signal objects that can be placed in two rows of these buttons. That is, for short names we can get up to near 100 signal objects. If the signal object is one, even this single base button is hidden.