[FIX] history merges may lead to an inconsistent mask

saqc/core/history.py

@@ -260,6 +260,9 @@ class History:
         value_hist.columns = columns
         value_mask.columns = columns
 
+        # clear the current mask
+        self.mask.loc[(~value_mask & value_hist.notna()).any(axis="columns")] = False
+
         self.hist.loc[:, columns] = value_hist.copy()
         self.mask.loc[:, columns] = value_mask.copy()
         return self