It can be duplicate of T252965.

Hmm, cannot reproduce in Firefox 78 on https://te.wikipedia.org/wiki/%E0%B0%95%E0%B0%B0%E0%B1%8D%E0%B0%A8%E0%B1%82%E0%B0%B2%E0%B1%81?veaction=edit&section=6&uselang=en after clicking the Map, clicking "Edit", and choosing "Map Contents" (@Arjunaraoc: please always include full and complete steps to reproduce!). Which web browser has been used?

@Arjunaraoc, this might caused by one of the gadget you have enabled. If possible, it would be great if listing all the gadget you are currently using, so we can find which gadget that cause conflicts with MediaWiki-extensions-CodeMirror.

In T258338#6317220, @Aklapper wrote:

Hmm, cannot reproduce in Firefox 78 on https://te.wikipedia.org/wiki/%E0%B0%95%E0%B0%B0%E0%B1%8D%E0%B0%A8%E0%B1%82%E0%B0%B2%E0%B1%81?veaction=edit&section=6&uselang=en after clicking the Map, clicking "Edit", and choosing "Map Contents" (@Arjunaraoc: please always include full and complete steps to reproduce!). Which web browser has been used?

My environment is
Ubuntu 18.04 (Budgie)
Firefox 68.10.0esr(64 bit) snap
Wikipedia gadgets enabled exlinks, Gadget-Twinkle,, Hotcat,Charinsert,Reftoolbar,

I have disabled the above gadgets, but the problem is still present.

In T258338#6317267, @VulpesVulpes825 wrote:

@Arjunaraoc, this might caused by one of the gadget you have enabled. If possible, it would be great if listing all the gadget you are currently using, so we can find which gadget that cause conflicts with MediaWiki-extensions-CodeMirror.

See my response at https://phabricator.wikimedia.org/T258338#6318055

I did not find the problem when using Chromium Version 83.0.4103.116 (Official Build) snap (64-bit). But it runs very slow on my system.

I have tried with firefox 78.0.2 (non-snap). I found enabling charinsert gadget is causing the cursor positioning problem when typing Telugu text.

In T258338#6318055, @Arjunaraoc wrote:

Firefox 68.10.0esr(64 bit) snap
Wikipedia gadgets enabled exlinks, Gadget-Twinkle,, Hotcat,Charinsert,Reftoolbar,
I have disabled the above gadgets, but the problem is still present.

In T258338#6318356, @Arjunaraoc wrote:

I have tried with firefox 78.0.2 (non-snap). I found enabling charinsert gadget is causing the cursor positioning problem when typing Telugu text.

Does that mean that disabling the CharInsert gadget fixes the problem in Firefox 78, but disabling the CharInsert gadget does NOT fix the problem in Firefox 68?

Sorry for my updates above, which were based on simple addition of text. But I found when I add Telugu text and then delete some characters, the problem remains in Firefox (68.10.0esr snap) , (nonsnap 78.0.2) and Chromium (83.0.4103.116) browsers.

Adding CharInsert based on previous comment.

With all gadgets disabled ,I checked on Windows 10, with Firefox 78, Edge version 18.18362, Chrome version 84.0.4147.89 and found the problem as most of my Telugu wikipedians use Windows. This needs to be fixed by mediawiki only.