Number of SLIP39 shares does not match the number entered by user

[romanzac]

Describe the bug
I had a problem during "Multi-share Backup" process (without a passphrase). Just after I confirmed my backup mnemonic on the device, I was asked for the number of shares and threshold. Number of shares got incremented by 1, once I confirmed it. When I tried again with number lower by 1, my shares check has failed on the second share. I was trying 2/3.

I had also a second (related) problem when I tried to create new wallet in multi-share backup (1/1) mode. This time the minimal threshold could be set only to 2 or more despite parts being set to 1. This problem was not happening when the wallet was created in "default" mode.

The 3/5 (default preset) worked well during "Multi-share Backup" process with passphrase.

Firmware version and revision
Trezor firmware v2.8.10, Trezor suite v25.7.4.

Desktop/smartphone setup (please complete the following information):

• OS: Mac OS Sequoia 15.6

To Reproduce
Steps to reproduce the behavior:
Please follow the video https://youtu.be/gHhRdofBb4M?t=383 The presenter found the same bug independently.

Expected behavior
Both "number of shares" and "threshold" remain unchanged after user input. Combinations like '3/2' which are invalid should stay invalid.

[obrusvit]

Hello, thank you for reporting this issue. It will be fixed in the September release.

It was already reported here #5099 and here #5581

As for the first issue (wrong number input):

As a temporary workaround, TS5 device will use the correct chosen number if you tap somewhere else (e.g. on the number between the +/- buttons) before you confirm the number input (i.e. tapping in the lower part of the display).

As for your other issue (creating 1of1 additional backup: I'll take a look.