Problem in PVP with picking up right char.

I want report a bug in PVP.
On my account I have 2 copies of same three star characters, one I keep on 165lvl and other on lower usually 40lvl.
From some time I cant use my second low lvl char in PVP fights, because when I choose him and I start fight It is always switched to loaner character 1/1/1.

I can use only loaner or my 165lvl char.

Please contact me if you need more information.