This behavior occurs on Android devices running 2.12.3 but I've noticed it on earlier versions as well. Just always thought it was my fumble-fingered typing.
Here's one that few people would likely see. It happens when setting the WebDAV address (or other text fields) in configuration on an Android device. If a mistake was made and you need to go back and fix it, the corrections are reversed as you type. As in
Start with the WebDAV address
note the cursor position. Now tap backspace twice and I end up with
The cursor should be just to the right of the dot but it's at the left.
Start over. Place the cursor back just to the left of the "2"
What's with the "dcba"?
Text is going into the line is the wrong place. Happens every time I have to correct my typing on the tiny screen but only on the configuration screen, not the markdown editor.
Most people can probably type on these screens so would not notice this, but I see it frequently as I have more than a few devices and like to change things often.
It does this on all my Samsung devices, A few examples Note10+ phone (Android 12/Gboard), an S20 phone (Android 13/Samsung KB), a Tab S7+ (Android 13/Samsung KB), Tab S6 (Android 12/Samsung KB), a Tab S4 (Android 10/Samsung KB) and even an old Tab A8 (Android 11/Samsung KB).
Perhaps it's a Samsung issue. Three different Android versions and two different keyboards and the only common denominators are Samsung and Joplin but it's only in that one section of Joplin that the issue occurs. Nowhere else on the device.
It's not a big issue but it is something that's been around for quite some time. Seems that when a character is typed the field gets the character and then backs up one position to maintain the same place relative to the beginning of the line. But only in that section of Joplin.