to reproduce: open an editor on android. Type in a line of text, composed of several words, without typing too fast. Try to use the "backspace" button to go back and delete text... Deletion gets "stuck" after a few characters, and cannot delete back further.
Not sure if Android support is a priority?
Just ran into this using Chrome on the Nexus tablet on Android 4.2.1. On certain inputs (kitchen sink/ asciidoc), the function of the backspace key alternates between backspace and forward-delete on each keystroke.
Firefox Beta 18.0 does not have this issue, but has other ones: Clicking in the editor will not bring up the keyboard once you have navigated away by closing the keyboard and/or switching to another app.
Both Chrome and Firefox work better if automatic spellchecking, correction, etc. are turned off.
Both have problems with voice input: Firefox inserts the input in duplicate, and Chrome just inserts the first couple of spoken words and reverts to keyboard input.
The backspace key doesn't work at all in Chrome on Nexus 4 and Nexus 10 -- just tried it on the editor on the landing page http://ace.c9.io/.
this should be fixed now see #1671