Thanks for trying.
It seems it's a Wine problem. I used the Windows version of Sigil with Wine. After every
save, the display went wrong on resume when I used EPUBs with embedded fonts.
When I use EPUBs without embedded fonts, nearly everything was normal.
Well, this version has now been deleted. I realized that the Linux version is no more the monster it once was (now 15 megs against 50 for the 0.34), so there is even no need for a portable version.