diff --git a/src/octoprint/plugins/softwareupdate/static/js/softwareupdate.js b/src/octoprint/plugins/softwareupdate/static/js/softwareupdate.js
index 9188a25a..b4feaeed 100644
--- a/src/octoprint/plugins/softwareupdate/static/js/softwareupdate.js
+++ b/src/octoprint/plugins/softwareupdate/static/js/softwareupdate.js
@@ -395,7 +395,7 @@ $(function() {
         };
 
         self.confirmUpdate = function() {
-            self.confirmationDialog.hide();
+            self.confirmationDialog.modal("hide");
             self.performUpdate(self.forceUpdate,
                 _.map(self.availableAndPossible(), function(info) { return info.key }));
         };
diff --git a/src/octoprint/plugins/virtual_printer/virtual.py b/src/octoprint/plugins/virtual_printer/virtual.py
index fa76a1a5..68c7b9e2 100644
--- a/src/octoprint/plugins/virtual_printer/virtual.py
+++ b/src/octoprint/plugins/virtual_printer/virtual.py
@@ -683,10 +683,13 @@ class VirtualPrinter(object):
 				pass
 
 		if duration:
-			slept = 0
-			while duration - slept > self._read_timeout and not self._killed:
-				time.sleep(self._read_timeout)
-				slept += self._read_timeout
+			if duration > self._read_timeout:
+				slept = 0
+				while duration - slept > self._read_timeout and not self._killed:
+					time.sleep(self._read_timeout)
+					slept += self._read_timeout
+			else:
+				time.sleep(duration)
 
 	def _setPosition(self, line):
 		matchX = re.search("X([0-9.]+)", line)
diff --git a/src/octoprint/server/__init__.py b/src/octoprint/server/__init__.py
index 68342342..f5dbbbd1 100644
--- a/src/octoprint/server/__init__.py
+++ b/src/octoprint/server/__init__.py
@@ -707,10 +707,25 @@ class Server(object):
 		preemptive_cache_timeout = settings().getInt(["server", "preemptiveCache", "until"])
 		cutoff_timestamp = time.time() - preemptive_cache_timeout * 24 * 60 * 60
 
-		def filter_old_entries(entry):
+		def filter_current_entries(entry):
+			"""Returns True for entries younger than the cutoff date"""
 			return "_timestamp" in entry and entry["_timestamp"] > cutoff_timestamp
 
-		cache_data = preemptive_cache.clean_all_data(lambda root, entries: filter(filter_old_entries, entries))
+		def filter_http_entries(entry):
+			"""Returns True for entries targeting http or https."""
+			return "base_url" in entry \
+			       and entry["base_url"] \
+			       and (entry["base_url"].startswith("http://")
+			            or entry["base_url"].startswith("https://"))
+
+		def filter_entries(entry):
+			"""Combined filter."""
+			filters = (filter_current_entries,
+			           filter_http_entries)
+			return all([f(entry) for f in filters])
+
+		# filter out all old and non-http entries
+		cache_data = preemptive_cache.clean_all_data(lambda root, entries: filter(filter_entries, entries))
 		if not cache_data:
 			return
 
@@ -741,11 +756,6 @@ class Server(object):
 					kwargs = dict((k, v) for k, v in kwargs.items() if not k.startswith("_") and not k == "plugin")
 					kwargs.update(additional_request_data)
 
-					base_url = kwargs.get("base_url", "")
-					if not (base_url.startswith("http://") or base_url.startswith("https://")):
-						self._logger.info("Skipping preemptive cache entry with base url {}, neither http:// nor https:// and possibly broken".format(base_url))
-						continue
-
 					try:
 						if plugin:
 							self._logger.info("Preemptively caching {} (plugin {}) for {!r}".format(route, plugin, kwargs))
@@ -758,6 +768,7 @@ class Server(object):
 					except:
 						self._logger.exception("Error while trying to preemptively cache {} for {!r}".format(route, kwargs))
 
+		# asynchronous caching
 		import threading
 		cache_thread = threading.Thread(target=execute_caching, name="Preemptive Cache Worker")
 		cache_thread.daemon = True
diff --git a/src/octoprint/server/util/flask.py b/src/octoprint/server/util/flask.py
index 40087c3a..4eb03131 100644
--- a/src/octoprint/server/util/flask.py
+++ b/src/octoprint/server/util/flask.py
@@ -430,7 +430,7 @@ class PreemptiveCache(object):
 					self._logger.debug("Removed root {} from preemptive cache".format(root))
 				elif len(entries) < old_count:
 					all_data[root] = entries
-					self._logger.debug("Removed {} from preemptive cache for root {}".format(old_count - len(entries), root))
+					self._logger.debug("Removed {} entries from preemptive cache for root {}".format(old_count - len(entries), root))
 			self.set_all_data(all_data)
 
 		return all_data