Kontact is designed to interoperate as well as is possible with a wide variety of groupware solutions. To that end, we sometimes make design compromises with respect to the various Internet RFCs that provide the basis for low-level libraries on which Kontact relies heavily.
We never knowingly violate any RFC.
The following list of RFC compromises is made by Kontact or the low-levels libraries used by Kontact:
When writing duration values into iCalendar files, Kontact never writes the DURATION property in terms of weeks (i.e., 1*DIGIT "W"); instead, the integer number of weeks is always multiplied by 7 and written in terms of days (i.e. 1*DIGIT "D").