apparently, setting a new geometry re-sets \intextsep

teckids2jahresbericht.cls

@@ -35,6 +35,9 @@
 \geometry{paperwidth=154truemm,paperheight=216truemm,includeheadfoot,top=7mm,bottom=7mm,twoside,inner=9mm,outer=7mm,nohead,footskip=5mm,showframe}%
 \makeatletter\f@nch@setoffs\makeatother%
 
+% restore lengths damaged during geometry change
+\setlength{\intextsep}{0pt}%
+
 % default licence for Jahresbericht is CC-BY-SA 3.0 or newer
 \dokumentLizenzCCBYSAthreeDE%