[Quoth]

Buttons are identical to each other on mine.
Either exchange it, or pop the back off with thumbnail or guitar puck starting at the fat edge diagonally opposite to the power button. It's not glued or sealed. The visible buttons are just plastic inserts sitting on top of the two "tact" type switches on the PCB.

The epub format IMO gives the SAME layout/format as other ePub ereaders or apps, or the epub2 converted to KF8/AZW on a Kindle (either by upload of epub2 to KDP to publish, not email to device, or local conversion and USB transfer by Calibre).
The kepub format seems to mess up if all sizes are not in "em", it may do "pt" sizes etc differently to the same file loaded as an epub.

Edit:
I have the same FW on a Kobo Touch -c, Original Aura H2O and the recent Libra. All do the format / layout the same with an actual epub2 file.