diff --git a/packages/mongo-livedata/oplog_observe_driver.js b/packages/mongo-livedata/oplog_observe_driver.js
index 098cf10eed..50f33aa679 100644
--- a/packages/mongo-livedata/oplog_observe_driver.js
+++ b/packages/mongo-livedata/oplog_observe_driver.js
@@ -28,11 +28,11 @@ OplogObserveDriver = function (options) {
     // There are several properties ordered driver implements:
     // - _limit is a positive number
     // - _comparator is a function-comparator by which the query is ordered
-    // - _unpublishedBuffer is non-null collection,
+    // - _unpublishedBuffer is non-null Min/Max Heap,
     //                      the empty buffer in STEADY phase implies that the
     //                      everything that matches the queries selector fits
     //                      into published set.
-    // - _published implements maxElementId method in addition to IdMap methods
+    // - _published - Min Heap (also implements IdMap methods)
 
     // We don't support $near and other geo-queries so it's OK to initialize the
     // comparator only once in the constructor.
@@ -159,7 +159,7 @@ _.extend(OplogObserveDriver.prototype, {
       var overflowingDocId = self._published.maxElementId();
       var overflowingDoc = self._published.get(overflowingDocId);
 
-      if (_.isEqual(overflowingDocId, id)) {
+      if (EJSON.equals(overflowingDocId, id)) {
         throw new Error("The document just added is overflowing the published set");
       }
 
@@ -202,7 +202,7 @@ _.extend(OplogObserveDriver.prototype, {
     if (self._unpublishedBuffer.size() > self._limit) {
       var maxBufferedId = self._unpublishedBuffer.maxElementId();
 
-      if (_.isEqual(maxBufferedId, id)) {
+      if (EJSON.equals(maxBufferedId, id)) {
         throw new Error("The document just added to buffer is overflowing the buffer");
       }
 
@@ -216,7 +216,7 @@ _.extend(OplogObserveDriver.prototype, {
     // To keep the contract "buffer is never empty in STEADY phase unless the
     // everything matching fits into published" true, we poll everything as soon
     // as we see the buffer becoming empty.
-    if (! self._unpublishedBuffer.size())
+    if (! self._unpublishedBuffer.size() && ! self._safeAppendToBuffer)
       self._needToPollQuery();
   },
   // Called when a document has joined the "Matching" results set.
@@ -468,11 +468,13 @@ _.extend(OplogObserveDriver.prototype, {
     // XXX needs more thought on non-zero skip
     // XXX "2" here is a "magic number"
     var initialCursor = self._cursorForQuery({ limit: self._limit * 2 });
+    var fetchedDocsCount = 0;
     initialCursor.forEach(function (initialDoc) {
       self._addMatching(initialDoc);
+      fetchedDocsCount++;
     });
 
-    self._safeAppendToBuffer = initialCursor.count() < self._limit * 2;
+    self._safeAppendToBuffer = fetchedDocsCount < self._limit * 2;
 
     if (self._stopped)
       throw new Error("oplog stopped quite early");
@@ -704,9 +706,10 @@ OplogObserveDriver.cursorSupported = function (cursorDescription, matcher) {
   if (options._disableOplog)
     return false;
 
-  // This option (which are mostly used for sorted cursors) require us to figure
-  // out where a given document fits in an order to know if it's included or
-  // not. We do it only if skip is not defined or 0.
+  // skip is not supported: to support it we would need to keep track of all
+  // "skipped" documents or at least their ids.
+  // limit w/o a sort specifier is not supported: current implementation needs a
+  // determent way to order documents.
   if (options.skip || (options.limit && !options.sort)) return false;
 
   // If a fields projection option is given check if it is supported by