It seems with the reverted version updated today, a new bug appears where changing bars causes ability icons to vanish.

Addon Version
10.2.12b

World of Warcraft Version
Retail

Example:

Same happens for me where if I dragon ride, the abilities that aren't set on the dragon ride bar are blank when I dismount

Same happens with druid forms. This was already a problem with dragonriding in beta versions but wasn't present in 10.2.11 and a few versions before that.
The previous "version" of this bug had the buttons reappear only when the corresponding keybind was pressed, now they become visible upon mousing over them.

Can confirm as well, only the first 5 buttons seem to always appear/display when mounting a Dragonriding mount (usually you have 6 dragon abilities with full talents) and after dismounting the action bar first 5 buttons appear/display, the rest only after you highlight them with the mouse or actually use them (they're still there but blank), similar case to #795 issue.

Confirming still occurs in 10.2.13.

This may be a bit better in 10.2.14