UX_DISPLAY render issue

[CedrikNikita]

While rendering arbitrary string, glitch appears.
It's shown in provided sample blue-app-samplesign. This code is used in our own repository.
Instruction of how to reproduce this glitch:

git clone https://github.com/CedrikNikita/ledger-sample-apps
cd blue-app-samplesign
make load
python demo.py

As a result you will see a glitch under the cross like that

[xchapron-ledger]

Closing it as this one is old and probably already fixed. Please reopen if needed.