strange bug in FontFamily from ttf file

* .NET Core Version: 3.1
* Windows version: Windows 10 (Version 10.0.18363.778)
* Does the bug reproduce also in WPF for .NET Framework 4.8?: Yes

**Problem description:**
I have to set TextBlock FontFamily from a static-name ttf file. everything is ok until i replace it programatically with another font file (it's about temp of some theme structure); then font callBacks to default. when i restart program it works again.

**Actual behavior:**
showing default font after replacing font file.

**Expected behavior:**
address static path to file and use, even if the file is not the primary.

**Minimal repro:**
https://github.com/qwerty13/Wpf-local-font-bug