From the fare rules of EK IEEESPL1 WAW to MLE:
Category 8: Stopover restrictions
2 STOPOVERS PERMITTED IN EACH DIRECTION
LIMITED TO 1 FREE AND 3 AT PLN 200.00 EACH.
1 FREE
3 AT PLN 200.00 EACH.
A STOPOVER MAY NOT EXCEED 30 DAYS.
The next more expensive fare EK CEEEFPL1 MLE to WAW says:
Category 8: Stopover restrictions
UNLIMITED FREE STOPOVERS PERMITTED ON THE PRICING UNIT.
A STOPOVER MAY NOT EXCEED 30 DAYS.
Even the most expensive fare EK JRRZFPL1 WAW to MLE has the same stopover restriction.
Also the First fares ex WAW that book in the A and F buckets have the 30 day restriction.