this bug appears since 2019.1.17.0 I guess -
using the filter in the navigation tree loose the focus after filtering.. so if you enter ABC, the focus is no longer in the box - rather the first entry in the navigation pane and you're unable to edit the filter string again - compared with 220.127.116.11 the focus is still in the filter box after filtering and editable.
I've reproduced the issue and opened a ticket to the engineering department.
For your information, the ticket number is RDMW-2678.
Thank you for reporting it!
Although our various support queues will be monitored for emergencies, Devolutions' offices will be closed on June 24 and July 1st, 2019.
The bug has been fixed internally. Starting from the next release of RDM, you will only lose your filter's focus after using the arrow keys or clicking somewhere else.