Looking at the changelog:
https://community.openvpn.net/openvp...gesInOpenvpn23

It seems they added a few changes about auth-user-pass in the latest releases

Something that may be related with your issue is:
https://community.openvpn.net/openvp...99d968d77c5ad/
https://community.openvpn.net/openvp...1702f1d0c2019b

After this, let me say that openvpn-applet has been tweaked a lot to manage user/pass authentication and has not been updated since 2010..
I hope someone would continue the development of this applet.

I'm using openvpn version 2.3.10 since some time and i'm going to push it to the autobuilder very soon.
I hope it could solve your problem.