Maybe I did not understand the issue you are reporting, and I have never tested that procedure the way you say that you have done, but really, why would you want the info (passphrase dots) to be accessible (cut/copy/paste) from the seed field?
Why would you want to edit/change/modify your seed inside the secret seed field, when you are not able to properly see what you are doing... see the character you are editing in any way?
I wonder if this is usual procedure for other people (as I have said, I have never considered doing so).
Why not edit it in a regular text processor, as it would be expected?
I may be wrong but, if I understood what you have reported correctly, I don't think "not being able to use the secret seed field as a text editor" is a bug at all, but actually it's a feature.
Sorry if I did not understand your report correctly.
Anyway, you don't really need to enter a different seed inside "new seed", when claiming, unless your old seed is malformatted.