PDF templates: custom font: Umlauts misaligned with respective letter

I have added a custom font (istok) to our pdf-viewer module (mpdf). It works fine except for one oddity:

Any text that:

  • is not read from a database field (but is hardcoded in html template)
  • flows over more than one line

shows its Umlauts (like öäü ÄÖÜ) not aligned with the respective letter. see screenshot.

Any text that comes from a database field (even if it flows over multiple lines) looks fine, and any short text that fits in one line looks fine.

Any ideas anybody? This didn’t occur with the standard mpdf font.