add @mandresm contributions to the fix

(cherry picked from commit 6a345ae)

src/esm_parser/esm_parser.py

@@ -2338,12 +2338,14 @@ def do_math_in_entry(tree, rhs, config):
     if "${" in str(entry):
         return entry
     entry = " " + str(entry) + " "
+    date_operation = False
     while "$((" in entry:
         math, after_math = entry.split("))", 1)
         math, before_math = math[::-1].split("(($", 1)
         math = math[::-1]
         before_math = before_math[::-1]
         if DATE_MARKER in math:
+            date_operation = True
             all_dates = []
             steps = math.split(" ")
             steps = [step for step in steps if step]
@@ -2421,14 +2423,18 @@ def do_math_in_entry(tree, rhs, config):
                     math = math + "all_dates[" + str(index) + "]"
                     index += 1
         result = eval(math)
-        if keep_list:
-            return ListWithProvenance(result, []) 
-        if isinstance(result, list):
+        if isinstance(result, list) and date_operation:
             result = result[
                 -1
             ]  # should be extended in the future - here: if list (= if diff between dates) than result in seconds
+        elif isinstance(result, list):
+            entry = ListWithProvenance(result, None)
+            entry.set_provenance(rhs.provenance)
+            return entry
+
         result = str(result)
         entry = before_math + result + after_math
+
     # TODO MA: this is a provisional dirty fix for release. Get rid of this once a more
     # general solution is worked out
     # ORIGINAL LINE: return convert(entry.strip())